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NIKOLA TESLA:
LECTURE BEFORE THE NEW YORK ACADEMY OF SCIENCES - April 6, 1897
Leland I. Anderson, Editor

TWENTY FIRST CENTURY BOOKS

BRECKENRIDGE, COLORADO

NIKOLA TESLA: THE NEW YORK ACADEMY OF SCIENCES
6, 1897

Nikola Tesla
International TelecommWlications Union

NIKOLA'TESLA:

BEFORE

THE NEW YORK ACAD8v1Y OF

The Streams oHenard and Roentgen and l\!ovel Apparatus lOr Their Prcxiuction

April 1897

Reconstructed

Leland 1. Anderson, Editor

1994

TWENTY ARST CENTURY BOOKS

BRECKEI\lRJOOE. COLORAOO

Copyright © Leland Anderson All rights reserved. No p'dlt of this book may be reproduced in any fonn
or by any means, electronic or mechanical, including photOCOpying,
recording, or by any mfOrmatIon storage and retrieval system, without
permission in writing from the publisher,

of

,,--,ll.;UV:': Card Number: 94-61004

ISBN 0-9636012-1-0(hardcover) 0-9636012-7-X (soft cover)

First Century Books P.O. Box 2001 Breckenridge, Colorado 80424

Contents

Figures

vii

Editorial

viii

ix

Introduction

xiii

Setting

1

on non-publication of

3

Lecture Commentary

7

High frequency apparatus

7

Lenard Roentgen

18

actions from Lenard and Roentgen

26

The

I -

29

Improved Apparatus for the Production of Powerful

Electrical Vibrations; Novel Frequency Measurement

Methods.

Section I Addendum

71

Wireless Telegraphy Receiving Methods.

Section II The Hurtful "\.-ClIVlli> of

83 Roentgen

""'''''''''Vll III The Source of "-'V''''''L)::;''H
and

95 Con-

Appendix

109

Contemporary reviews of lecture

III

Acknowledgments

117

VI

CONTENTS

Sponsorship

118

Index

121

vii

Figures

Form of listing: Sec. !f.-Fig. If

LC
I-I
1-2 1-3 1-4 1-5 1-6 1-7
1-8 1-9
1-10 !- I I 1-12 1-13 1-14 IA-I5 IA-16 IA-17 IA-18 IA-
111-
1lJ-2 111-3
111-4

node in

circuit)

14

Method of transformation of electrical energy by oscil-

34

latory condenser discharges

Mechanical

of electrical oscillator

35

illustrated in

I with self-induction coil

37

Coil wound to secure

increased r.,,,,,,r:lfv

37

a secondary coil with a primary circuit coil

38

System

for existing

circuits

38

Circuit controller allowing condensers connected to dis-

39

charge circuit

and ~ll<~~~~~.v~1

H"'5"""v"" of parts and circuits of a small oscillator

39

of small oscillator diagrammatically shown

41

8

Apparatus for the manufacture of condensers and coils

46

High potential coil system having terminals at centers

48

Photograph of coil system illustrated in

II in action 52

instrument to

determine

and phase 62

Method of impulse illumination of instrument disk

67

Devices for

'72

Other ways of

73

interrupter)

74

74

(A series of six photographs of drawings of 120 bulbs exhibited on walls of New York Academy of

76-81

Illustrating an experiment

the

rays

the real source of

97

Improved Lenard tube

102

arrangement with improved double-focus

103

tube for reducing

actions

Illustrating arrangement with a Lenard lube for safe

106

working at close range

viii
Editorial Remarks

Section I of this lecture is presented with few changes from

the original text

by Tesla, an illustration of which

is reproduced on page 30. The text would have benefited

an editor's hand if presented to a publisher at that

but no such editorial "smoothing" has been attempted in

presentation now. Only minor changes have been intro-

duced, such as in words that were separated before the turn

of the century but now appear solid. They are: electro-

magnetic, electro-motive, in as much, foil, wave

length. few articles and prepositions were missing, and

their

have set in brackets []. As

an additional to the reader, certain items have been

marked brackets with an explanation provided in a note.

figures 13 ab, 14, and 16, together with the

photographs of drawings of 120 bulbs

76-81, have

Section I appeared among a group of papers passed on to

children by George Scherff, who was Tesla's personal

secretary, business manager, and confidant from 1895

through

A also

in the archives of Tesla

Museum

copies,

were mISSIng

some illustration drawings and photographs. These were

drawn from the archives of Knight Brothers and Boyle

Anderson.

Preface

Nikola Tesla was born of

parents at Smiljan, the

Austro-Hungarian border province of Lika, now part of

Croatia, at midnight July 9-10, 1856. His father, Milutin,

was a Serbian Orthodox priest, and mother, nee Djouka

Mandie, was a family line whose sons were the clergy

and whose daughters were wives of the clergy. Serbian

Orthodox church then used the Julian calendar, and it con-

tinues to use this

today for days observance. The

American colonies converted to the Gregorian calendar

years before

arrived at York in 1884. When

crossed 'date ' 11 days dropped his per-

sonal calendar. Most institutions observe Tesla's birth date

as

10, which date

held for himself, but if the

tolling church

Lika could have heard in Ameri-

ca when Tesla was born, the calendar date would have been

July 21,

Establishing himself in United States,

became a

in 1891. brought to the world great'

gifts

for which he

induction motor and the

multi-phase alternating current power distribution system

driving it (1888); the fundamental system wireless

raphy embodying "Tesla coil" (

(1898); the Tesla turbine (1913-20), which attracting great

interest; and, among many leading inventive achieve-

VTOL

(1928).

* The Tesla family moved to nearby

when Nikola reached the

age of six to enter school. Adding to the uncertainty of the date accord-

ed Tesla's birth is an official certificate of birth entered for him by the

city Gospic

his birth date as June 1856. certificate

is reproduced in Nikola Tesla:

with Relatives (Bel-

grade: Nikola Tesla Museum, 1993; in Serbian and English), illus.

sec. I thank Milan Radovic,

of Wisconsin-Madison Li-

braries. for translating this ~'61HH',all'

x

PREFACE

50

following the presentation of the principles

wireless telegraphy now called

at his

in

Teslaasserted inventive claim. It wasn't until five

months following death in 1943 that the United

Supreme court declared the basic radio patent Marconi in-

valid,

the prior art of Tesia for system con-

cept and apparatus, Stone the method of selectivity, and

Lodge variable tuning.

In his lifetime, Tesla was granted over 30 honorary degrees

and foundation medals from the world over. The unit

magnetic flux density in the MKS system was named "tesla"

on the occasion of the centennial year of his birth. The only

other

to share such recognition is Joseph

The 1897 lecture before the New York Academy of Sciences

was the sixth historic lectures delivered in rapid succes-

sion in America and in

The previous five lectures

were:

of Alternate-Current Motors," May 16,

of the American Institute Elec-

in New York

followed by the

trio series of demonstration lectures on high frequency and

high potential alternating currents, the first,"Experiments

with Alternate Current of Very High Frequency and Their

Application to Methods of

Illumination," May

20, 1891, before a meeting of the

New York City;

the second, "Experiments with Alternate Currents of High

Potential and High Frequency," February 3, 1892, before

the Institution of Electrical Engineers, London, followed a

day

(with some condensation) by special request at

the Royal Institution, and by invitation, February 19, be-

fore the Societe Internationale des Electriciens and the So-

ciete Francaise Physique; and the third, "On

and

Other

Phenomena," February 24, 1

before

Institute Philadelphia and (with

some variation) March 1, before a meeting of the Nation-

al Electric Light Association in St. Louis (it was in the

latter that the principles of radio

commUnI-

cation were first presented); and

and

cal Oscillators," August 25, 1893,

a meeting of the

PREFACE

xi

International

Congress at the Columbian Exposi-

tion in Chicago, and (with some variation) November

before a meeting the New York Electrical """'1-""

delivered four additional ''''''''.'Ull,,"' lectures or

in

absentia, the last in 1911.

--e

Introduction
There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy. Hamlet, Act I, Scene 5
In 1895, the fluorescent coating of a cardboard screen offered just enough illumination for Professor Wilhelm Conrad Roentgen to find his way to the discovery of the X ray. The implications of his discovery for the medical profession were, of course, no less than staggering. Yet history has shown that its implications for the world of physics were more far-reaching than anyone could have imagined.
At the time of Roentgen's discovery, many scientists were quite comfortable with the Newtonian explanation of the way the universe worked and even discouraged students from pursuing careers in physics because, as they thought, physics offered little career potential: almost everything already had been explained! A few notable exceptions, among them black-body radiation and the Michelson-Morley experiment, challenged the neat and simple explanations of Newtonian physics, but the world of science was confident that these phenomena soon would be understood. The nature of light and electricity (ether waves vs. radiant matter) and the structure of the atom were still in the question-forming stage. Roentgen's discovery of the X ray signaled the end of two centuries' confidence in Newtonian physics. With little reservation, the discovery of the X ray can be considered the birth of modern physics.
Where, boundless nature, can I hold you fast? Faust, 455
The trail leading to the discovery of Roentgen's invisible light began in the seventeenth century with two chance observations of visible light: Von Guericke noting that a

xiv

INfRODUCl'ION

faint glow occurred between his hand a spinning sulfur

ball Piccard finding that light is

from mercury

sloshing around the top a barometer. By the early eigh-

teenth

Hawksbee, knowing that a vacuum had been

present in upper part of Piccard's barometer, constructed

glass vessels removing some the air. He excited them

with frictional electricity and observed beautiful glowing

streams of colored light. Almost a century and a half passed

before the real significance of this

accelerated

would begin to be

The 1790 introduction of Volta's electric battery allowed

Oersted, Ampere, Faraday, and Henry to deduce the rela-

tionship between electricity and magnetism. Page

Rhumkorff

induction

the high voltage

transformers, which could increase the few volts from a bat-

tery to many thousands volts. In the

Geissler

veloped an efficient vacuum pump, similar to Piccard's

which employed the weight of

to pull

the air out of a glass

a glass blower, fabri-

cated many types of

tubes, evacuated them using his

own new pump, and watched them glow with beautiful col-

ors when high voltage from induction coils was applied.

Variations in the

composition, the kind of gas, and the

level of vacuum were used to expand the multicolor effects

of Geissler tubes.

equipment improved, higher vacuums were attained;

PlUcker, Hittorff, and Crookes observed streams of light

emanating from the negative electrode of some of their dis-

charge tubes. Furthermore, a magnet was seen to bend and

deflect this stream, called the cathode ray. Crookes, Gold-

stein, and Perrin designed many variations of vacuum

charge

most of which demonstrated new

of

cathode ray. Magnetic-effect, paddle-wheel, and canal-ray

tubes were only a few of such types.

In the nineteenth century, true nature of cathode was a subject of much controversy. In 1803, Thomas Young showed that light had a wave nature and many scientists assumed that cathodic light (one name given to cathode rays) was just another light wave traveling in the ether. However, Crookes, among others, saw cathode ray as a

INfRODUCTION

xv

stream of matter particles which termed "radiant matter."

In 1890,

constructed an

in which cathode

were found to exit a

through a thin

aluminum

His untimely death

In

left his student,

with task of continuing

their experiments. Lenard

Roentgen to repeat some of

the experiments that Hertz he had conducted and pre-

sented Roentgen wi th some

with which to accom-

plish them.

many

scientists of his day, Roentgen focused on

the cathode ray. On the evening of November 1895, he

carefully covered a discharge tube with a black cardboard to

prevent the light in tube from

with his

gation. Immediately upon energizing the

Roentgen no-

ticed a greenish glow emanating from a nearby cardboard

screen that

been

with a chemical compound

known to

in the

of cathode rays. Cathode

rays had never been known to journey more than a cen-

from rnA',,,,,,",,"

tube, and

the cardboard

screen was more than a

distance from tube,

Roentgen concluded that the glow he

was the

feet of a new kind of During the course of further

"-""'V", Roentgen

to

his

to

as he held sman lead fishing

in front the dis-

tube: shadow the bones in his

were

cast on the fluorescent cardboard.

The

discovery was made. Given certainty that

rays were being produced in

quantities by

the discharge tubes in use at the time, X rays might have

discovered by any number of scientists during the pre-

vious several decades. Rather than diminishing Roentgen's

achievement, however, this

it considerably,

demonstrating not only

genius in

what was happening but his

in stopping to

On December 28, 1895, Roentgen published about

copies of preliminary paper and distributed them to

local colleagues in Bavaria. Early in

he made an-

nouncement to rest of the world.

The of

living

bones tissues their

bodies was disconcerting to most people, to say the

xvi

INTRODUCTION

A New Jersey

proposed a bill to outlaw the mak-

ing of

opera glasses, while a

manufacturer

offered X-ray-proof undergarments. In Roentgen's own

culture, the sight of bones presaged imminent death, and

Roentgen's wife was horrified by the

in hand.

Obviously, the most immediate application of the new

covery was in medical world, and medical practitioners,

scientists, and instrument companies

any information

they could get. Crookes-type vacuum discharge tubes and

induction coils were not easy to find outside of university

physics laboratories. A Boston dentist, William 1. Morton,

actually made use of a simple light bulb connected to a bor-

rowed induction coil to produce some the first X-ray

ages in the United

On

11, 1896, the New

York Electrical Review answered the

for information

about X rays by launching a

of eight

by Niko-

la

in which he presented many new ideas, inventions,

and

dealing with the ray, its production, use, and

explanation.

The

What is the craze,

The town's ablaze

With the new phase

of

ways.

Wilhelmina Electrical Review (London)
17, 1896

Anderson's reconstruction of Tesla's lecture before the New

York Academy of

on April 6,

is a most

portant contribution. In this

Tesla went beyond his

titled

"The Streams of

and Roentgen

Novel

for Their Production," and expanded on

his X-ray articles published in the

York Electrical Re-

view.

large

of his vacuum tubes were

displayed on the walls of the

halL

the tubes

re[)re~;entea were not only Crookes and

types but va-

of single-electrode tubes of Tesla's own invention,

some of which were used for his Roentgen-ray demonstra-

tions accompanying lecture.

INTRODUCTION

xvii

During lecture,

discussed the uses of some of

tubes in his experiments with wireless telegraphy. Among

his tubes,

said, were "a great number of

de-

"Compare this statement with

1916

re-

by Anderson in first book of this series, Nikola

On His Work With Alternating Currents: "Well, in

some of these bulbs I have shown, for instance, that a heat-

conductor

a stream

or as I said at that

charged particles, a few of

bulbs have been

exactly in the same manner the audion is used today."

is prompted to ask, "What was Tesla really

in his research and experimentation with vacuum

tubes?" His statements about using the tubes in the receiving

and detection of wireless

offers clues. his

ture before the Academy,

often referred to Lenard-

Roentgen-streams and tubes; obviously considered

Lenard and Roentgen to hold equal

in the

of X The Lenard tube, as well as

mentation, were of particular interest to Tesla that '"""'""""'"'"

rays (streams electrons) actually emanated from the alu-

minum window opposite the cathode of tube and pro-

ceeded a centimeters into air.

research by

Corum and Kenneth Corum indicates that Tes]a was

looking for methods of moving electrons with such devices

as open-air diodes or even relativistic electron-beam (REB)

diodes, which, if

as they are built today, including

power supply, resemble closely a Tesla coil and a Lenard

tube.

speculation about Tesla's moving electrons is,

perhaps, only the

of the story. Other

particularly his

on particle beam weaponry, points

to interest in moving larger

Another great value Anderson's contribution in recon-

structing this leeture is that it shows us historically the extent

of Tesla's work with vacuum tubes up to 1897. Roentgen's

announcing the discovery the ray

Tesla with

yet another area in which to contribute discoveries and

inventions. This lecture on the rays Lenard and Roent-

and Tesla's series articles in New York

Review contain material far more advanced than any

other contemporary work.

1897 lecture discussion

of "reneeted" Roentgen

offered with data tables,

xviii

INfRODUCTON

almost exactly to Arthur H. Compton's 1922

monograph on the topic of secondary radiation.

offered a design apparatus to generate "reflected" rays.

lecture is a fount of information beyond the knowl-

edge of most of his contem}X>raries,

a wide array of

tables, charts, diagrams, photographs,

designs,

and suggestions of one process after another for the produc-

tion of X rays, the use of vacuum tubes, and special

dures for refining the operation of all kinds of apparatus.

Tesla, here and in other works, discussed scientific princi-

ples not "discovered" until years later.

The most significant contribution of this text .rerhaps,

that it shows in his true light one of

Vlslonanes

that ever

man far ahead of his peers yet gentle and

willing to give what he had to the world. With regard to the

relationship between Tesla's work and the world of ",-,<,-,u","

it is curious to note that it has taken a better part of the last

100 years since his invention of the resonant

for

to truly

in duplicating the

coil

sign, this in spite of the great pains went to in making his

recommendations clear. Let us hope that, as more informa-

tion on Tesla's work becomes available, much greater atten-

tion will be

to it, to the betterment of our world.

Jim Hardesty Judith Hardesty Ithaca, New York
June 1994

cannot help looking at that little bulb of

Crookes with a feeling akin to awe, when he

considers all that it has done for scientific pro-

gress-first, the magnificent wonderful achieve-

ments of Roentgen. Possibly it may still contain

a grateful Asmodeus, who will be let out of his

narrow prison cell by a lucky student. At times it

has seemed to me as though I myself heard a

whispering voice, and I have searched eagerly

among my dusty bulbs and

I fear my

imagination has deceived me, but there they are

still, my dusty bulbs, and I am still listening hope-

fully.

N, Tesla
March 7. 1896

Background

Setting

1897

the New

Academy of u\./I'",11'-"",,:)

did not appear in entirety in Tesla's lifetime. In an extend-

ed 1916 interview he remarks,

lecture was not published

I had to a lot

of things. I had undertaken an extensive program, and I

found that my energies were not adequate to the task.

Later on, the subject was neglected; other business

vented me from doing anything

It only

typewritten form, uncompleted.,,1

original

as delivered, carried title,

"The Streams Lenard and Roentgen and Novel Apparatus

for

Production,"2 but actuality it went far beyond

that topic. On the walls of the

hall Tesla displayed

proximately 120

drawings of vacuum tubes that he or-

dered built in

by his laboratory technicians.

Many of these were of Lenard type and also the single-

electrode type pioneered by him and used demonstrations

of

methods in lecture. Among the drawings were

tubes

wireless telegraphy experiments. The hereto-

unpublished portion of the 1897

text cov-

ers, with

of

on X-ray

NikoJa TesJa On His Work With Alternating

Currents and Their Application to Wireless

Telephony,

and Transmission of Power (Denver: Sun Publishing, 1992), p. 158.

(Editorial) "The New York Academy of Science: An

Electrical Exhibition--Address Nikola Tesla announcing recent

achievements," Electrical Review (N.Y.), Apr. 14, 1897, p. 175;

"Mr. Tesla on

Rays," p. 398, and (Review) "Mr.

Tesla

the New York

of

"EJectricalEngineer,

Apr. 14, 1897, pp. 400-401; the latter was published under the title,

"Mr. Tesla on X Rays," in the Electrical Review (London) May 7,

I p, 626. See Appendix for reproductions of these reviews.

3 The term "X ray" had not, at the time of this lecture, been generacceptc!<l for the rays of Roentgen.

2

BACKGROUr...TD

discovery, high frequency resonators and measurement

methods. In addition, Tesla

an extension of the

measurement topic into wireless telegraphy receiving meth-

ods which is

as an Addendum. These topics are

not suggested

title.

It is concluded that subject matter the lecture specifi-

covered by its title was published over

name in

communications entitled ''Tesla on the Hurtful Actions of

Lenard and Roentgen

and ''Tesla on

of

Roentgen Rays and

Practical Construction

Safe

Operation Lenard Tubes," Electrical Review (N. Y.),

May 5 and

11, 1897, respectively.

portions

of the lecture immediately follow the Addendum. With ex-

ception the first five introductory sentences of the

communication referencing the lecture before the Academy,

the

segments plus added

from the 1916 inter-

view

the Addendum) allow one continuous reading as

the complete lecture.

outline of the

lecture is as follows:

Improved Apparatus the Production of Powerful

Electrical Vibrations; Novel

Frequency Measure-

ment Methods.

Section I - Addendum

Wireless Telegraphy Receiving Methods.

Section II

Hurtful Actions Lenard and Roentgen ...."'1"' .."'.... III

The Source of Roentgen Rays and the Practical struction and Operation of Lenard Tubes.

There are perhaps two combining reasons why the lecture

was not published

entirety as delivered.

as points out

of the IVV'.Ulv

and in the 1916 interview,

to the intense research

engineering activity he was at that time

Some of

THESEITING

3

include (a) crystallization of his

telegraphy, telephony, and transmission of

of patent coverage; (b) the

on

wireless-controlled telautomata; (c) the development high

intensity phosphor-coated vacuum-tube

the fluores-

cent lamps today; (d) time-consuming task

his patent

courts.

The second reason relates to the growing, highly competi-

tive atmosphere in wireless telegraphy development now

recognized as radio.

at that applications for

the fundamental patents in

teiegraphy,4 undoubt-

edly realized that detailed information contained in this

of the

(presented as

I) was of propri-

etary

and it would given away without first obtain-

ing protection through patent applications. Whereas Tesla

had giving freely to the world many technological ideas,

In

his

trio series

delivered

in 1891,

and 5 he now grew more cautious, and

rightfully so, in protecting his own economic interests in the

field of wireless communication.

Skirmishes on non-publication of lecture

that

In United

weekly I'Arnm,"',.",

electrical journals were published: Electrical

Electrical Review, Electrical World, Electrician, Electricity,

and Western Electrician. In addition to these were week-

ly

American, which reported on a mix of scientific

as well as monthly

periodicals Electrical

and Engineering

4 U.S. Patent No.

of March 20, 1900,

of

Transmission of Electrical

" and U.S. Patent No.

of

May 15, 1900, "Apparatus for Transmission of Electrical Energy,"

both applications filed

2, 1897.

5 Martin, T.e., The Inventions. Researches and Writings of

Nikola

(New York: The Electrical

1893), chs. 26-28

(pp. 145-373).

4

BACKGROUND

Magazine.

early publication activity was primarily a

the vast electrical industrialization

and

opportunities that sprung from inventions

in the direct-current realm and, subsequently, the

inventions of Tesla in alternating-current realm. The mar-

was unquestionably

electrical news

coverage, and commercial electrical journals fought to

alive.

Thomas Martin, serving as president of the American

Institute of Electrical

for the

under-

took editorship of Electrical World in December 1888 but

was discharged in March 1890 over a

dispute with the

owner the publication on compensation. The feud was

aired on seven tabloid-size pages in the September 30, 1893

6 Martin subsequently found a

as editor of

Engineer.

In

the

Company published the

book, The Inventions, Researches and Writings of Nikola

Tesla, compiled by Martin, chief editor. This

re-

mains a classic a century later having been republished sev-

eral times.7

years before death Martin remarked in a letter to

Thomson,

some money out my

book, which was promptly borrowed from me by the titular

component, so that two

of work went for nothing."g

The

Company was undoubtedly in

financial condition as the letter

offered to Martin in lieu of cash receipts

book.

6 I am indebted to Marc

his forthcoming work,

The TesJa Trilogy, for this revealing insight concerning Martin's business relationship with Tesla.

7 The firs I reprint was undertaken in 1952 by the Lee Engineering Co. of Madison, Wise., as a contribulion to the engineering industry.

8 Jan. 16, 1917, in Selections from the Scientific Correspondence

of Elihu Thomson, Abrahams, R.J., and

M.B., eds.

bridge, Mass.: MIT

1971).

SKIRMISHES ON NON-PUBUCATION OF LECfURE 5

During the year prior to the 1897 Academy Sciences lec-

ture, the Electrical Review published a remarkable series of

communications from Tesla in the journal on the sub-

ject of material stream emanations.9 Not to be outdone,

Martin presumably persuaded Tesia to have the Academy

lecture published in the Electrical

But

obvi-

ously had second thoughts for reasons

Martin, perhaps not fully appreciating the role an inde-

pendent inventor depending for his

upon suc-

cessful marketing of patented inventions, could not accept

decision to not complete the lecture for publication.

Martin had a ravenous appetite for

to make the

Electrical Engineer financially successfuL The following

year, Martin allowed to published in November 17,

1898

without permission, TesIa's paper, "High

Frequency Oscillators for Electro-therapeutic

Other

Purposes," presented

the eighth annual meeting

American Electro-Therapeutic Association in Buffalo,

New York, September 14, 1898. An editorial salvo entitled

"Mr. Tesla and the

also appeared in the same issue-a

sort of 'tit for tat' rejoinder on the non-publication the

Academy of Sciences lecture-together with a specific pa-

editorial, ''Tesla's Electrical Control of Moving

Vessels or Vehicles from a Distance," dwelling on the im-

practicality of his recent invention. 10

Martin certainly went beyond professional ethics in publish-

ing the lecture. Undoubtedly, the stress of financial

problems of the Electrical Engineer was too trying. He need-

ed 'leading-edge'

and Tesia was not producing it.

9 "Tesla's Startling Results in Radiography at Great Distances

Considerable Thickness of Substances," Mar. 11, pp. 48, 49;

"Tesla's Latest Results," Mar. 18, pp. 146, 147; "Tesla on Reflected

Roentgen Rays," Apr. 1, pp. 171-174; "Roentgen Radiations," Apr. 8,

pp. 183-186; "Tesla's Latest

Investigations," Apr. pp.

206-211; "Tesla Describes an

Feature of the X-Ray

Radiation," July 8, p. 43; "Roentgen Rays or Streams," Aug. 12,

pp. 78, 79, 83; and "Roentgen Streams," Dec. 2, pp. 277, X.

10 U.S. Patent No.623,809 of Nov. 8, 1898, "Method and Apparatus for

Controlling Mechanism of

Vessel or Vehicles," application filed

July 1, 1898.

6

BACKGROUND

Tesla was furious

unauthorized publication

prior to the opportunity given the American Electro-Thera-

peutic Associatlon to publish in its Transactions, II and sent

copies of his severe

to all electrical journals in

America and

Electrical Engineer also carried

the letter with accompanying defensive commentary running

four columns in the November 24 issue.

To understand the

crisis facing the Electrical

Engineer, one must ahead another three months to March

11, 1899, when

Engineer was taken over

the Electrical

merged publication becoming

apr...."',rn World

Martin was retained, but as

co-editor.

temperament, he perhaps did not

perceive

as did others. Years later, in

fiftieth

of

Engineering, the

fidal journal

Martin's misadventure with

Electrical Engineer was not mentioned.

It should not

that Martin held a

grudge toward

even though later promoting 'U~"''''''Jl

in articles. Martin was too much of a gentleman to such

professional competition interfere with true friendship.

the wound the failed Electrical Engineer required some

years to heal.

book
Story of may truly of electrical

Frequency Oscillators for

and

" American Electro-Therapeutic Association Tnmsac-

9-29. This paper has been reproduced by

First

Breckenridge, Colo. (1994).

12 "Nikola

"Feb. 1894, pp.

and "Tesla's Oscillator

and Other Inventions," Apr. 1895, pp. 916-933.

Lecture Commentary

High frequency apparatus

On March 1895, Tesla's laboratory at South Fifth

(now West Broadway) in New York City was com-

pletely destroyed fire-all

lecture

apparatus, photographs,

documentation. Charles

Dana editorialized,u

The destruction of Nikola Testa's workshop, with its wonderful

contents, is something more than a

calamity. It is a mis-

fortune to the whole world. It is not in any

exaggeration

to say that the men

at this time who are more

to

the human race than this young gentleman can be counted on the

of one

perhaps on the thumb

hand.

On December of this same

Wilhelm Roentgen

1923) presented his communication, "On a New

of

" to Wtirzburg Physico-Medical Society,

the news

newspapers 11 days later.

It was a

significance, ability to

"see" images through otherwise

bodies, for which

he was awarded the first Nobel

in physics in

......"',"'-'u I of

that follows, Tesla describes de-

tail his researches along the same lines undoubtedly

would have him to the same discovery were it not for the

circumstances of destruction his laboratory

Edward Hewi tt, philanthropist given an interesting account of Tesla's lost opportunity. 14
During his experimental researches ill photography, Hewitt

13 The SII11 (New York), Mar. 1895, p. 6. c. 5.

14

N.F., "Trout Fishennan-Sportsman of the old school,

R. Hewitt calls himself 'last of the gentlemen mechanics,'" Life, July

15,

pp. 86-100. See also reference to Hewitt's working with

Tesla on

photography in Thompson,

Roe11tge11 Rays

(N.Y.: D. Van Nostrand,

1896) p. 157. Hewitt is mentioned by

Tesla in his April 22, 1896 communication to the Electrical Review.

8

LECTURE COlvt:MENTARY

describes a morning in Tesla's laboratory

the fire

when attempting to photograph Mark Twain under a

Geissler tube. IS The resulting print was instead of the

camera lens adjusting screw! Hewitt notes that neither he

nor Tesla realized, until

when Roentgen made

his announcement,

this was an X-ray photographic

Image.

As the title of scri bed many quency, high and Roentgen
evolution the grarnmati call y
mechanics and spark-gap corno()nents ated with the COIl0emSjeI employed analogic of the systems there are certain limits
electromagnetic ....u'""""J, general agreement. 17

Beginning with Section 1, Tesla ticaJ operation of powerful, high

3 and extending through figure 8 of innate understanding of the prac-
resonant-coil systems to produce and high potential alternating

15 For a oratory, see Century

of Mark Twain with Tesla in his lab"Tesla's Oscillator and Other Inventions,"
pp, 916-933 (photo appears on p. 930).

16 U.S. Patent No.

of Nov. 3, 1891, "Method and

Apparatus for Electric Conversion and Distribution," application filed

Feb. 4, 1891.

17 See

"Jedno uopstenje zakona 0 centralnim sila-

rna 0 odnosu Nikole Tesla i Dordem Stanojevica" (A Generalization

on the Law of Central Forces About the Relation Between Nikola

Tesla and

in

"Nikola

grelr>-;:,mulanjuvo'IJ''-'' July 7-10, 1976, pp.

I In this

certain analogy problems in science and

cOITespoIldence between Tesla and physicist

en~;ap,f:d in the discovery of aucuv;;,,,,,

gravitational, magnetic, electrical, electro-

Ha~~H"'U". ~IJ'''''.''. botanic- and biologic-cell, and planetary fields,

HIGH FREQUENCY APPARATUS

9

currents.

design of physically small-size coils

operating from existing municipal circuits is discussed, es-

pecially those for use in physicians' offices then supplied

with 110 volts

current or 60/125 cycles secondl8

alternating current. Such

were widely

by physi-

the

1900s for electrotherapeutic

19

7, Tesla has in-

circuit allow-

ing the alternate charging and discharging independent

condensers in the primary circuit from the power source. He

also

to a modification of this circuit having "one con-

tinuous contact common to two circuits, and independent

for

these," allowing not only an alternate

charging discharge of condensers but their simulta-

neous charging and discharge in parallel. These circuits are

V'V,","\#V in Tesla's United States patent No.

of

1897 (application filed Sept. 3, 1896). The

importance this technique was obviously not recognized

by those '>tt.:>,nr1, the

was the heart of Tesla's

later work on what

to as the "art of individualiza-

tion" and embodied in invention known today as the

AND logic gate.

Coming to diagram

8, the layout of circuit ele-

ments is

for the desk-top coil unit shown in

which

offered use in operating X-ray

and

various laboratory appliances. unit stood 18 inches high

at discharge terminals and comprised several novel

tures giving an energy conversion efficiency of 80 percent.

months later, when Lord Kelvin attended a meeting of

the British Association the Advancement of Science in

18 Although the unit "Hz" for frequency is now universally "U~'P"'U

for

measurement, at the time of publication of this 1897 lec-

lure, and for some eight decades later, "cycles per second" was the unit

of measurement. To avoid reading inconvenience

Hz in editorial

discussion and

per second in the lecture text, cycles per second

(cps) will be throughout this work.

19

High

Electric Cur-

rents in Medicine and

(N.Y.: William R.

Co.,

N.M., A Working Manual of High Frequency

Currents

New Medicine Publishing Co., appearing in

editions from 1911 to 1923).

10

LECfURE COl\1J\1ENTARY

Science in Toronto, Tesla

units to him

on the occasion of his

Street

tory in

York City.

several of

units, and later proceeded to enter a business venture

with a Mr. Hopkinson for the manufacture of a sizes of

and X-ray units, but information about the establish-

ment this business enterprise not been located.20

next briefly describes work phosphor-coated

bulbs to

the incandescent-filament bulbs developed

by Edison. became interested developing a lamp that

would equal the intensity of sunlight, and in January, 1894,

the first photograph taken in Tesla's laboratory by light only

from his phosphorescent lamp appeared in the April, 1895

of the Century Magazine. It was an eight-minute ex-

posure, but a little more than two years Tesla had

achieved such brilliance in lamps the May 20, 1896

issue of Electrical Review (N.Y.) carried an illustration

of a two-second photograph Tesla taken with a lamp

of candlepower-again by the light of bulb itself.

Such a result with the combination of the eXisting

emulsions and indoor lighting had not before been achieved.

This single-electrode lamp, first shown by Tesla in 1891

first of trio series lectures

in

America and Europe during the years 1891-93 - was patent-

ed by him that

21 Following this

demonstra-

tion, Elihu Thomson filed a

of

Lighting"

patent application that was determined to in interference

with Tesla's patent.

laboratory

that

he did actually produce operating lamps with a

con-

ductor and lead-in

However, Thomson was unable to

prove such a demonstration, although asserting earlier

on the

subject, and his claim was therefore

Patent Office declaring Tesla's priority in this

vention.22 In an unpublished statement entitled "Tesla's

Artificial Daylight," written by Tesla and designed to secure

20 Tesla letter to University Libraries).

Scherff, Oct. 13, 1905 (Columbia

21 U.S. Patent No. 454.622 of June 1891,

of Electric

'-'115'L"I115'" application filed Apr. 1891.

22 U.S. Patent Office Interference No. 17334, Thomson vs. notice filed July 12, 1895, decision of priority to Tesla June 10, 1897.

IDGH FREQUENCY APPARATUS

11

investment in a company to manufacture of mination were

application this form of

[interior

lamps and

are not only

they are also

from

disadvantages as, the large cost

installation, which is chiefly due to the

quantity of

copper required; the frequent

of the lamps,

owing to their unavoidable deterioration; the disagreeable

,.,n<''''''I"''''''' of the

which,

a small sur-

is naturally too intense

to the

the necessity employing more or less opaque

screens, which involve a considerable loss in illuminat-

power, and many other drawbacks of this nature. It

is true, that recently Nernst and

have

some gain in efficiency of incandescent lamps or

by use coatings of rare

which

mit higher degrees incandescence. this departure

not done away the objectionable features above

mentioned-on the contrary, it has added to them.

In

new lighting system, all

disadvantages

are successfully removed. The light is produced with a

smaller

of energy,

more

one eighth of

is presently

the same

quantity of

it is soft and

to the

closely

offers

tures of an ideal

of any de-

candlepower may be adapted to any kind of

current of supply, and they last indefinitely."

We find that Tesla, one the early energy conservationists

in engineering, was

a number of lighting

parata found in use

prominently fluorescent-lamp

All

lectures from

cessity completely

air bubbles

and coil units of high frequency, high

oscillators. Not only amateur

but professional engineers

overlooked the harmful destructive

in such

components.

on the necondenser disruptivern"'n"'''.~ and
have allowing

12

LECTURE CO~NTARY

the destruction of a

used in a

power was

quickly,

than raising the primary

over days, allowing the coils to "cook"

the oil bath. well, most amateur

not taken the diligent,

of their systems to

It is often expressed,

Tesla

achieve

brilliant resul ts? - I seem not to be able to re-

produce them with the same effectiveness as he claimed,"

the

of Sciences lecture,

found it

in some detail the

which

success by describing a

of insu-

lating

and inductor

a manufactur-

ing sense.

method was

then two

months

the lecture

excluding air

or from the dielectric separating

of high

potential in

proximity, or remote portions of the same

conductors, in as perfect a manner as

and in a con-

venient practicable way.23 In

all rolled-foil

having waxed-paper

were manufac-

a modification of the method

describes and

by the Cornell Dubilier Company.

11, Tesla diagrammatically shows a pair of sec-

wound wi th turns

their mid-

point

brought out as a

unit de-

signed to withstand the encapsulation

exerted by

the manufacturing process previously

Tesla

U1...(\."".:> a significant statement

the length of sec-

coil windings, that each

to or some-

than a quarter wavelength electromagnetic prop-

in the winding, thus allowing a maximum potential

at ,the terminals. As such, these coils represent a

paIr.

on to describe the critically
"'V11"-,111 Poggendorff (

of the spark gap in the early investiga-
on the action of a

23 U.S. Patenl No.

of Feb.

Electrical Condensers, Coils. &c.,"

HIGH FREQUENCY APPARATUS

13

in a vacuum/4 and suggests various

the design of the

in the

the necessary attention to the construction of the

to

produce currents of high voltage and frequency "causing

showers or continuous streams of thick, thundering sparks

to dart out into space to a distance of 8 or 9 ... some-

times veritable lightning bolts." Many readers today, in

looking at the photographs of the discharges that Tesla pro-

duced in his laboratories, usually do not consider din as-

",,-,,-,.au..,u with such displays. Tesla has made

in

other writings to wearing ear plugs, and it has been reported

that the noise from his experimental station at Colorado

could

10 miles away.

An element of "the discoverer's

searching

1S

found in observing an "exaggerated Thomson

,,25

noticed the pnmary circUlt of

copper ribbon,

the inactive portion of which should be no more than five

percent, is perceptibly cooler

heat

parently carried away from the

to the

coatings of condenser. Of

Tesla coils

constructed

then, no reports

in open

on this subtle, difficult-to-measure effect.

Another aspect of primary circuit, as was found for the

secondary circuit, is critical attention to length. Tesla

that as as a quarter of an inch change in length

of the primary circuit will have a pronounced effect on the

performance of a coil!

advocates that best

is

a''''Ul1~''''' when a stationary wave is fonned with a single

24 Poggendorff, J., "Effects of Interrupting a Current Within Dis-

charge

.. Philosophical

4th sec., Vol. 10, I

pp. 203-307.

25

Britannica

(1

defines the

Thomson effect as "the evolution or absorption of heat when electric

current passes through a circuit

of a

material that has

a temperature difference between two points

its

This

transfer of heat is superimposed on the common production heat by

currents flowing through conductors because of their electrical resis-

tance. If a copper wire carrying a steady electric current [i.e., direct CUf-

rent] is subjected to external heating at a short section while the rest re-

mains cooler, heat is absorbed from the copper as the conventional CUf-

rent approaches the hot point, and heat is transferred to the

beyond the hot point."

14

LECTURE COtv1MENTARY

node located at a point of the discharge circuit or conductor equidistant from the opposite condenser coatings, as illustrated below.

L,

b,

5

L,

b,

With this design, a half-wave primary circuit length results. This may be difficult to achieve in practice for the construction of Tesla coil systems as revealed by the table shown below. For the desk-size unit illustrated in figures 9 and 12, for example, the operating frequency would be in excess of SOMc.

Operating frequency of secondary
10 kc 50 "
100 " 500 "
1 Mc
l 5" 10 " 50 "

Length of primary to achieve halfwavelength 9.3 mi 1.9 " 4,900 ft 984 " 490 " 98 " 49 " 10 "

It is obvious that for a secondary coil constructed as above, and the primary constructed according to the same design criterion as described earlier, both coils will have nearly the

HIGH

APPARATUS

15

same length and, essentially, the same number of turns-a

1: 1 turns ratio. It

at first

"How do we

tain

not

from the secondary/primary turns

the Qof the coils and a standing-wave condition that results

in coils appropriate length also contribute substantially to

Although significant resonant can be achieved

in a transformer having a 1: 1 turns ratio from high Q values

and properly adjusted length primary and secondary

coils, such design is rarely undertaken.

The desk-size units illustrated in figures 9 and req~i~e

careful design of the primary

operating

mumCI-

supply circuits of 110 volts, to obtain high current exci-

tation of the primary coil. half-wave circuit loop from the

condenser coatings is a unique way to accomplish But,

when a high-voltage, high-current supply is available,

then the advantage of higher numerical values for secon-

dary/primary turns ratio (approximately the square root of

respective inductance values ratio) prevails.

Tesla advocated that the length of a grounded

coil

should be a quarter wavelength of the oscillation frequency,

yielding the maximum potential at its terminal by virtue of a

standing wave condition. The first of design

was a photograph appearing in May 20,

the New York Electrical Review showing Tesla

seated

an 8-foot diameter flat-spiral coil his labora-

tory on Houston Street but without accompanying explana-

tion. During this

Tesla provided two diagrams

showing these flat-spiral

in experimental wireless

transmi tting and receiving antenna circuits, again without

explanation. 26 following this lecture,

applied for

his first

on wireless telegraphy

such coils

technique, now universally employed,

for quarter-wavelength radio transmitter antenna circuits.27

Oliver Shallenberger, known for his development the induction ampere-hour meter in 1888 for the Westinghouse Electric and Manufacturing Company, which had committed itself to alternating current power equipment production by

26 See Sec. I-Addendum, 27 See note 4.

15 and 16, pp. 72, 73.

16

LECTURE COMMENTARY

acquisition of the "famous 30"

patents on motors and

systems, contributed infonnation that has not appeared

where

the high frequency,

voltage appara-

tus used by

in obtaining the

presented in

first of 1896 X-ray communications to the Electrical

Review. 7JJ

which are especially

important, it may be

that the current was taken

from an alternator, of a frequency of periods per

second, passed through a primary coil of a trans-

fonner for increasing the e.mJ. from 100

to from

16 to thousand. The secondary current was then

passed through Leyden jars and a double cascade of

slightly separated brass cylinders, whereby it was

changed an oscillatory current of an extremely high

frequency, which was then connected through the

ry of a second induction coil having very few turns of

wire, no iron core and having a ratio of 7 to L By

this means the

was

to

between

160,000 volts to

was used to energize the

discharge

the generation of X rays."

we find that for driving experimental evacuated tubes,

employed resonant-coil apparatus preserving a frac-

tional wavelength for the secondary,

than the

The detennination of exact operating frequency oscillators

was a vexing problem for all early investigators, a difficulty

those today working with

having

time-base

may not fully appreciate. Wave

essentially a closed oscillatory circuit,

with

substitution inductances and variable

were

used in the near

of WWL29 But before the tum of the

century, experimenters and

devised their own

ad-hoc methods of frequency detennination.

In this lecture,

a carefully calibrated {1P',''''''

he did not push to patent but for which the diagrams

7JJ Thompson, E.P., Roentgen Rays--and the Phenomena of the

Anode and Cathode (D. Van Nostrand, 1896), pp. 136-138.

29

for

Mauborgne,

Practical Uses ofthe Wave

Meter in Wireless Telegraphy (Mc-Graw Hill, 1913).

l-llGH

APPARATUS

17

presented in lecture clearly indicate that a patent was con-

The patentable

of device was the "visual

synchronism" capability in reading divisions or markings

a unifonnly rotating disk illuminated with

flashes

from neon or spark sources associated with the system to

measured. device is

today as the electronic-

stroboscope pioneered by Harold Edgerton (1

1990).

The mechanical

fork, a tuning fork with slit

shutter, been used others unaware of Tesla's

tion until about 1910 for uniform motion measurements.

When this editor showed Dr.

a copy of a portion

this lecture revealing

much earlier

with stro-

boscopes using neon and arc flash illumination,

replied

no claim invention of the concept.30

disk shown

Fig. has 10 radial

segments on the outer ring, with radial segments 9, 8,

6 the succeeding inner rings. Note that in Fig. 14,

the outer ring is further subdivided into 10/20 divisions per

segment with a

adjacent to that ring.

Let r be the number of revolutions per second, s the number

of radial

in the ring, and a and b

integral

(I, 2, etc.). If the frequency of the flashes differs

from r(s·a/b) by lib cycles second, then a·s radial seg-

ments will appear to revolve at a rate of 1 radius

per

second. Thus, a disk of s radial

illuminated

b·s flashes

each revolution appears a disk having

b·s

if flashes occur sib times for

revolution, the disk appears to have s radial segments.

this method to used as a detection scheme, it is dear

that presence of continuous-wave

would not

of sufficient strength to excite a small neon flash lamp, typi-

cally requiring 90 volts for ignition. Tesla describes

asing the circuit containing the lamp to near ignition with a

battery pack. A number these detection circuits are to

found in Tesla's

patent and in a pair of

30 Personal communication, Feb. 1988.

18

LECTURE COrv1MENTARY

means and methods detection patents issued

ceeding four

31

the suc-

The method of synchronous rotating disks or

employed by

in continuous-wave

and presented

from 1901 to

was the

receiving methods in

with visual synchronization measurement and de-

tection schemes, publication of which would preempt

patent disclosures, that undoubtedly caused

not to

commit this portion of lecture to publication.

Lenard and Roentgen rays

The discovery of vances achieving discovery of the William Crookes with various residual gas
pressures of a few pink streamer is observed fills the entire cross duced. At about rate into identifiable
proceeding from anode at the other

U.S. Patent Nos. 61

of Nov. 8, 1898, "Method and

for Controlling Mechanism of Moving Vessels of

" application filed July 1, 1898; 685,954 of Nov. 5, 1901;

"Method of Utilizing Effects Transmitted Through Natural

"

filed Aug. 1, 1899; and

"Apparatus for

Transmitted Through Natural 1899.

.. application filed Nov. 2,

32 U.S. Patent Nos.

of Nov. 5, 1901, "Method of Inten-

and Utilizing Effects Transmitted

Natural

"1'1>11'-""")" filed June

1

of Nov. 5, 1901,

Effects Transmitted From a Distance to a Receiving

Natural Media,"

filed Sepl. 9, 1899; and

of April 18, 1905, "Art

Electrical Energy

Through the Natural Mediums," application filed May 16, 1900.

HIGH FREQUENCY APPAR.A.TUS

19

the Crookes dark space (in German literature, Hittorff dark space), negative glow region, Faraday dark space, and lastly the positive column with striations are observed. It is the positive column that is seen in neon signs operating at several millimeters of pressure.
Lowering the pressure from 0.1 millimeters of mercury, the Crookes dark space lengthens with the striations in the positive column becoming farther apart. At roughly 0.08 millimeters, the cathode dark space reduces in length to about l centimeter. The Crookes dark space, negative glow, and Faraday dark space regions will remain fixed in length along the tube with the positive column taking up the remaining length of the tube regardless of the tube's length. At pressures substantially below 0.01 millimeter, a green Iluorescence appears on the inner walls of the tube, and below 0.001 millimeter, the tube becomes dark.
As an aid in evaluating the degree of vacuum obtained for the Lenard and Roentgen tubes that Tesla investigated and demonstrated, when a vacuum is on the order of 0.001 millimeter of mercury the X rays are easily absorbed, minimally passing through the human hand. These rays are referred to as soft X rays, roughly a few angstroms in wavelength. At 0.0003 millimeters of mercury, exceedingly high voltages are needed to produce a discharge and the X rays are quite penetrating, able to pass through the bones of a hand with little absorption. These rays are referred to as hard X rays, about 0.1 angstrom in wavelength.
It is significant that Tesla considered both Lenard and Roentgen rays in his communications and lecture regarding "penetrating rays" through substances. Some astonishment was expressed by radiologists of the results Tesla achieved in his experiments not only at the time they were presented in the lecture and in his 1896-97 communications appearing in the Electrical Review but as well by those reviewing these reports many years later. This is primarily because Tesla's researches involved both Lenard and Roentgen apparatus, as the titles of his reports so state, but his communications on the subject ha\'e generally been interpreted in terms of only X-ray apparatus and effects.

20

LECfURE CO:tv1MENTARY

In briefly reviewing "rays"

it is noted Philipp

Lenard (1862-1947), in 1893, announced discovery of

invisible rays produced a Crookes and capable of

passing through a thin aluminum window. Now known as

"Lenard rays", these are

beams capable of

passing

window

The

thin aluminum window

become known as a

"Lenard window," in his experiments penetrating

were produced at the point of first impact-the window.

Lenard, Roentgen,

or other researchers knew

what they were dealing with in terms of "rays" up to that

time.

as well as other

were at the fore-

front investigation, undertaking researches to answer

fundamental

of the nature of rays particles. In

the Academy of Sciences lecture, Tesla demonstrated a

source of powerful rays which he

as more nr\,cx",.,r_

ful than any before available.33 The source of the

was

an arc

closely-spaced electrodes in vacuum, now

recognized as extreme ul traviolet radiation (approx. 500

angstroms). The ability to distinguish soft X

and ex-

treme ultraviolet was then difficult.

But 1897

a new era

of the sub-atomic

identified electrons

mass, elm, and

lated.

physics

calcu-

Kelvin was in opposition to the evolving theories of

atomic structure advanced Thomson, Rutherford, and

others. was greatly influenced, for most of his lifetime,

by the

of Rudjer Boscovic (1711-1787), an extraordi-

narily remarkable scientist who

in engineering, ar-

chitecture, and archeology.34 Of Boscovic

remarked

an unpublished 1936 interview article,

33 Refer to Appendix for a review of the lecture April 1897.

in the

....Aauu.,'lljl:5 the life and work of Boscoof the 200th anniver-

HIGH

APPARATUS

21

relativity theory by

is much older than its

nri"CP''1r proponents. It was advanced over 200

ago

by my illustrious countryman Boscovic,

great

philosopher who, not withstanding other and multifold

obligations, wrote a

volumes of

lent literature on a vast

of subjects. J...I""£","<1'

with relativity,

so-called

conti nuum...."

1884 Baltimore

35 referred to

36 and in 1890s adopted Boscovic's

terpretation forces, the "force curve." When

Thompson published the discovery of the electron

1897, Kelvin extended the concepts Boscovic to

of electrons accounting for all

phenomena and ra-

dioactivity-a model explaining

ejecting at

velocity_

not

Tesla's contemporary

writings on

but acknowledged years later, the theo-

ries of Boscovic and Kelvin had influence on his

pretation of experimental

obtained.

Let us

some of the

results described

Tesla in his researches during

period.

rectly

that the source of

rays is

place offirst

of the

stream of particles

in the bulb."37

familiar

of today, the rays

emanate from a massive anode

inside a tube bombard-

ed by an

stream of electrons a heated cathode

under high potential difference. anode target is,

this case, place of first impact of particle streams pro-

duced inside tube.

In his

"On Reflected J.''-'''''lHi~''''U Apri I 1, 1896 Electrical

35 Baltimore Lectures on Molecular \LA!UUvu. Cambridge

and the Wave 1904).

36 Theoria Philosophire Naturalis redaeta ad unieam legem virium in natura existentium (Venetia: Editio Venetia prima ipso auctore prresente, et corrigente, 1763).

37 See Section III.

22

LECTURE COrvtMENTARY

qualitative description of the intensity of rays which he interpreted to be reflected from a dozen metal and nonmetallic surfaces. He also reported that the relative strength of the re-radiations from the various metals agreed with the sequence of these metals in the activity series developed by Volta. At that time, the phenomenon of secondary radiation of X rays had not been hypothesized. It was not until 1922 that Arthur Compton presented in monogra~h form a definitive analysis of secondary X-ray radiation. 8 It showed that Tesla's series of the relative strength of what he interpreted to be "reflected rays" from various metals agreed with the mass absorption coefficients for these metals when excited by soft X rays; i.e. in the region of 1 angstrom. The following year, the first successful reflection of X rays with a very small incident glancing-angle of the radiation was reported by Compton, thus revealing the experimental difficulty.
Tesla found no evidence of X-ray diffraction, but a dozen years later research apparatus became available providing W.H. Bragg, Max von Laue, Ernst Pohl, and Bernhard Walter the opportunity to show diffraction. As well, Tesla found no evidence of refraction. In 1925 the first successful experiments showing refraction were reported by Larsson, Siegrahn, and Waller. 39
A review of the Academy of Sciences lecture finds Tesla stating he had succeeded in deflecting Roentgen rays by a magnet- the rays also charging a condenser at some distance. oW But in his communications appearing in the April 22 and August 12, 18% issues of the Electrical Review, he modifies his remarks saying Lenard rays could be deflected by a magnetic field whereas Roentgen rays could not as observed by exposure of fluorescent-emulsion films. Thus, he identified a distinction between them in their producing penetrating rays. When the energy of Lenard rays is abruptly
38 Compton, A.H., "Secondary Radiations Produced by X-Rays,"
Bulletin of the National Research Council, October 1922, (Vol. 4, Pt. 2, No. 20), the third and last of a series which formed the report of the Committee on X-Ray Spectra.
39 Larsson, A., Siegrahn, M., and Waller, T., "The refraction of x rays," Physical Review, Feb. 1925, p. 235.
oW Refer to Appendix for a review of the lecture appearing in the EleclricalEngineer, Apr. 14, 1897.

HIGH

APPARATlIS

23

by a magnetic

from a bulk I"ytt'rt'."

source or an individual atom, as in passing through a

window or in the bombardment of a massive

nomenon bremsstrahlung radiation results.

Bremsstrahlung is observed moving with radiation a motion."! From
apparatus, X explainable result.

for light particles such as

through matter. par-

that

di-

descriptions

with

by bremsstrahl ung is an

The tubes that Tesla

one

a cathode.

in his researches had only remarked,

if we put two

in a bulb ... , we limit

for

"""""'11"''''' not only of the anode but

any conducting

the

practicable JX)tential on

for such a tube, sion stream emanating
at the other

place of first cathode would tube.

an emlsthe glass

appearing in the March 18, 1896

describes obtaining

shadow

at a

distance of 40

if it as-

that X rays were produced at the

envelope at

of the tube, that would not fully account the abil-

ity to obtain X-ray

graphs at such a

distance as

40 feet.

most interesting a tube to
ously produced:

were, in the main, wi Lenard rays

through a thin aluminum window,

that could not distinguished

or molecular

He gives a

the

process in

point where

are

f we attach a fairly exhausted

an elec-

trode to the terminal of a disruptive coil, we observe

41 Feynman, R.P " Lectures on Physics (Reading, Mass.: 1963,

Addison-Wesley), Vol. 1 of 3, p. 34--6.

42 E1ectrical

March 11, 1896.

24

LECTURE CO.M1v1ENTARY

small streamers breaking through the

of the

Usually such a streamer will

through the and

crack the bulb, whereupon the vacuum is impaired; but,

if the seal is placed above the terminal, or if some other

provision is made to prevent the streamer from passing

through the glass at that point, it often occurs that the

stream breaks out through the side of the bulb, produc-

ing a fine hole. Now, the extraordinary thing is that, in

spIte of the connection to the outer atmosphere, air

cannot rush into the bulb as long as the hole is very

at place where the rupture oc-

curred may grow very hot-to such a degree as to soft-

en; but it will not collapse,

bulge out, showing

that a pressure from the inside

than that of the

atmosphere

On

I have ob-

served that

bulges out and the hole,

which the streamer

out, becomes so large as to

perfectly discernible to the As the matter is expelled

from the bulb rarefaction increases and the streamer

and less

whereupon the

es again, hermetically sealing opening. process

of rarefaction, nevertheless, continues, streamers being

still visible on the heated place until the highest degree of

exhaustion is reached, whereupon they may disappear.

Here, then, we have a positive evidence that matter is

being expelled through the walls of the

,.,43

This curious process, in its examination a near century later,

that the internal

was

the resul t

an internal force.

operated his single-electrode bulbs

at extremely high voltage, high frequency currents. An elec-

tron beam develops at the cathode as a result of high-field

emission during the negative half of the

current

cycle.44 It concentrates on a point

at the

end of

the tube arising

either localized ionic stress, trace im-

purities, or a high

of dopant additives. The

43 Electrical Review, March 18, 1896.

44 For a discussion of the internal process of

bulbs

excited by

frequency, high voltage alternating currents, see

Corum, J.F., and Corum, K.L., "Critical Speculations

Tesla 's Invention and

of

Electrode X-Ray JJll''''"'''AI

Discharges for Power Processing,

Resonances and Particle

Beam Weapons,"

of the 1986 International Tesla Sym-

posium, Colorado

pp. 7-21 - 7-44.

HIGH

APPARATUS

25

spot then becomes a virtual

because of temperature

between annealing and melting points (variable

with ~lass composition, approx. 4S0-S00°C and 1

I ,SOO C, respectively), resulting in significant conductivity

to the outer surface in contact with

dispersed-medium

return of the high voltage source impressed on the cath-

ode. When a point

color, its specific re-

",,,,,<1,11'_'-' can drop from 100 trillion ohm-centimeters at room

temperature to 10,000 ohm-centimeters at annealing tem-

perature and unity at the

point. using such ex-

tremely high voltages on

and single-electrode tubes,

Tesla advises in his communication appearing in March

18,

issue of

not to overheat them

In continued use.

This editor has viewed a video an experiment performed

1985 by

Dollard showing the same process a

single-electrode bulb developing a hot spot, the glass bulg-

ing out, rarefaction increasing, and bulb subsequently

resealing. This process yet to critically investigated.

Tesla's December 1896 communication to Electrical

Review refers to a "material

projecting from

single-electrode bulb and he later remarks,

to

wonderful gun, in-

deed, projecting

of a thousandfold greater pene-

trative power than that of a cannon ball, and carrying probably to distances of many miles, with veloci-

not producible in any

way we know of."

This germinal idea of projected particle

in air, the

succeeding experimental work undertaken in Colorado

Springs 1899

extremely high potentials and the

of

electron beams, undoubtedly crys-

Tesla's

approach a particle-beam weapon

he

to the allied powers as WWII storm-

clouds were gathering.cls

45 This design

appears in

of the Tesla

Centennial Symposium, Colorado Springs, 1984, pp. 144-1

an abbreviated fonn for unit expressions: e.g., acceleration vAl"''''''''"''"'

simply as "meters" rather than umelers/second2." A of this

"1J1J'V<l\vil is as well held by the Tesla Museum in

26

lECTURE COMMENTARY

Hannful actions from Lenard and

tubes

were

of lecture that Testa did

to publish

form of two communications appearing in the

May 1 and August 9, 1897 issues of the Electrical Review

(Sees. II and III of this reconstructed lecture) on the subject

of felt an

actions from Lenard and necessity to present
those undertaking ....",,,,.:,..,,1'>

tubes. He medical

dangers in the

l"''''''U''Ull experiments

the body-exposing a

the hand be(.:on11

swollen. Believing

a mechanical injury, he

thrust his

hand dose to window of the tube and instantly pain.

The pain lasted a days afterward and later he observed

that all the hair was destroyed and that the nails on hand

had grown anew. describes the tightening of

or

stiffening of

when a hand is held dose to win-

dow of the

In a sever case, the skin gets deeply

ored and

places, and ugly, ill-foreboding blis-

ters form~ thick

come off, exposing raw

discharges

pain, feverishness

When

unknown

the human

who either inadvertently or

known

experiments having uncer-

tain outcome to

taught the valuable lessons from

which we benefit

a result of the harmful

Tesla experienced, continues in these communications

advocacy for the proper construction and shielding

apparatus with particular concern for medical

and patients.

Tesla was the constant
trical inventor and
Thomson nor (later acquired by cessful in challenging

of Elihu Thomson, an
of the period. Neither
Electric Company Company) were sucWestinghouse Electric and

HARIvlFUL ACTIONS

27

Manufacturing Company on the Tesla

for alternating

current

distribution systems motors. The scene

courts \vas all too

walking in,

in

attire

his attorneys, and as a witness

astonishing court and ",,,,,,,,,,,,"v,,,rC' with a

dis-

of recan and caustic wi t.

biographer shows at-

tempting to elevate

by misstatements of

cerning subject's competitor or adversary.

biographer, David Woodbury:16 saw

Columbian

demonstrating Tesla's

of alternating current

distribution a nonevent- Thomson presumably had

accomplished the various

demonstrations!

In an

i

Thomson

X rays,

Abrahams and Marion

in their compilation of

son's correspondence,47 engage in unbecoming

distortion by entering a surprisingly impertinent ref-

erence note for a letter from Dr. William Greene to Thomson

dated December 20, 18%, mentioning an

burn suf-

fered by Thomson on his finger during

editors mention Thomson's "lively controversy with

Tesla who thought that X rays were

." No

such an exchange on the

of harmful

X-ray radiation, but a lively exchange did occur between

six years prior to the

of

lecture on

the nature effects of high frequency currents. Although

beneficial the

readership in providing an airing

of the

it appeared at the expense of Thomson.48

reconstructed

of

lecture follows. It is

now seen as a contribution to the history of

scientific

and

elOiprrienrs

period not previously nt''''''''"

LJ.A

46 Woodbury, D.n, Beloved Scientist (McGraw-Hill, 1944).

47 Selecrions from the Scientific sou (see note 8).

of Elihu Thom-

48 The exchange occurred in a succession of communications to the

Electrical World following the

in its Feb. 1891, issue

of the first of Tesla's trio-series

on high frequency alternating

currents: Thomson, Mar. pp. 204-5;

Mar. 21, pp.

Thomson, 4, p. TesIa, Apr. 11 , pp. 272-3.

I haunted thee where the Ibis From the Bracken's crag to the

Tree.

N. Tesla
November 4, 1934

Section I

IMPROVED ApPARATUS FOR THE PRODUCTION OF Pow-

ERFUL

VIBRATIONS;

HIGH

CY MEASUREMENT

.L.a\J1,"," & Gentlemen:

You will still

vividly, no

the

which a year ago was

by the announcement of the

discoveries of Professor Roentgen. Suddenly, without any

preparation, Roentgen surprised world with two won-

derful results. showed us how to a photographic

impression of an object invisible to the and, what

seemed more extraordinary, enabled us, the help of

his luminous screen-now known as the fluoroscope-to

see, with our own

outlines the object. We are

living in an of exceptional intellectual activity, and im-

advances are often recorded, but

were almost

the order of the telescope and

and such dis-

come no more than once or

in a century.

Scarcely can anyone of us hope to again witness in his life-

time an event of so widespread a scientific and popular inter-

est.

desire to see things which seem

hidden

from sight is more or

strongly developed in

human being,through all degrees of this sentiment, from

curiosity the unenlightened to the absorbing

for knowledge of highly refined, and this in

sufficient to engage universal

apart

these discoveries brought promise of

to

sufferers and

allover the world the fibers humani-

ty. It is hardly necessary for me to tell you that the

hold of me also, mine was a singular, grave case,

I had not recovered from its effects to this day. I hope

you will pardon

a slight digression which I have a

strong reason to

30 THE STREAMS OF LENARD AND ROENTGEN
and not so m"~h those of in: and~scer.: t 'V:ICU'.I1II t:.bes, al~houeh s~e phot0i;n.i'hs ...er~ 11;';11",15<1 taJc.:n wI;!! these. As bo~h the art1s~5 and m. Gelt were b~5~' on other IMt~ers t he plates 1n t!!6ir ordinar, holders ...·ere trequcntl:l·pl.lt in 110:118 corner of ~h~ labora~or,· i.lntil
II 5"itab}" o.?portunH,; tor carr;;1ns on the expQl'imcn ts was t;)Und,
Dt;.r1ng these invest191tions mall}· plates gave a res"lt, wMla m«nJ others falled. and on s.me of these hoth :!r. Alle::. 'lilt,) then asdshd me, lind myselt noted unacoountable marks ar.d defects. Ur. Alle# partlcularl# tound It ~~trllordlnar, that, In $~lte of his <:"r8, l!I<l.nj. plates proviid defective and unsucoEUtul. The :a;:lng ot
th.se photograph!.:: !l!IP ressions bJ means ot Crook~s bulbs br)u"ht
freshli to m:; mind the el<Per1l11~na of Lena.rd, $Ot:le teat;.;.res of 'IIb!ch, partiC'... ll1rl.l the action on a sensitive plate, had hs~lnated
me trca the start, and 1 resol ved to go over the ground CO'/flred IIi
him with assistance and improved ,-pplianees. Just a6 my at.ent.ian RII arrested II;, this teat;Jre fD:j laborlltory with almost ever;,t:;J.ng it contained was destroyed; end the few!'!lonths toUOlilnc passed in inhnn ac:1v1t;r w'hic!! made lIIe temporarily torget :fi;I projects.
had hardlj' finished the work ot reconstruction and resU:led th~ course ot III;; lde~s when the ne..,. ot Roentgen's IIchievement reae~d
me. Instantl;r th e truth flashed upon my mind. hurried to rep eat h15 incilmpl ete1;; repo rted e~per1men~. and. th ere 1 lIehel~ the "onderm;,selt. ~hen -too lata- 1 realized that::tJ;J g.lldJ.ng IIplrl~ had ag&in pro",pteo. me lind ~h;.!t 1 hlid till 1 ed to c.",pr"hend his .",:;s~erl-
Reproduction of lecture text page.

SECTION I

31

the close of 1894,

the necessity

a straining task, on which I have been laboring

number of years and which commands my

to me to

actinic action of

The

did not appear to

and I began the work at once, securing later, at the

of some

connected with the Century

Magazine, the assistance of Messrs. Tonnele & Company,

artists' photographers, of city, then doing work this

'"1';"''£''.11'"', In these experiments, I employed an for the production of powerful electrical

as well as one of my

alternators of

A

variety

without external electrodes were

fact was soon brought to

that the

power the Crookes bulbs

varied

and that some, which emitted a comparatively

strong luminosity, hardly showed an effect, while

of

much

light-giving power, produced strong

I wish to state here, in

to be clear, that

forts were directed toward investigating such actions true

phc)spltlorescent light, as

bulbs without

of heat, and not so much those of

a~;cel1t vacuum tubes, although some photographs were

with these, As both the artists and myself

were busy on other matters, the

in their ordinary hold-

ers were frequently put in some comer of the laboratory

until a

opportunity for carrying on the experiments

was found. During these investigations many plates gave a

result,

many others failed, on some of these

Mr. Alley,

then assisted me, myself noted unac-

countable

and defects. Mr.

particularly found it

extraordinary, in spite of his care, many plates proved

defective

unsuccessful. The

of these photo-

graphic

by means of

bul bs brought

freshly to my mind the experiments Lenard, some

tures of which, particularly the

on a sensitive

plate, had

me from the

I resolved to

over the

covered by him with assistance and

proved

Just as my

was

by this

32 THE STREAMS OF LENARD AND ROENTGEN
it contained

and

news of

me. Instantly the truth

his incompletely

wonder myself.

too late-I realized that my

spirit had again

me and that I had failed to comprehend his myste-

statement of these facts might

misinter-

at the time of Professor "V1~"lj"\v"

I have kept silent, although I was

my feeling in the introductory

articles I wrote on this subject in

fnl""'nr-,nf Review. Presently, however, I

misunderstanding of my works, and I am

my

painful but stimulating experience

to

some of

those, who have lightly written

of this new

more

appreciate this new

I was quite

with the results of

naturally

of his beautiful and promising experiment;,

possibility of the plates being marked and

by some action of the bulbs never

to

my mind.

some might see in this only an

for my own shortsightedness, others, more kindly

towards me, will with myself, consider it

a

stration

great words, which I will not

in

the

which say that, what Nature

not want to

mind, one cannot force it

it was always since my ever, that I have not been
who then communed with me, but that, on further guided me and guided me
of the nature of these marvelous mani-
in bringing to your attention some new

SECTION I

33

facts which I have

discovered in addition to those

already announced, I may induce, at least some of you, to

interpret these

as I do. For though, that I

might

my chief

this

I must your

kind indulgence to dwell in a few works on the novel appli-

ances which are exhibited for inspection. When I

trace their

I find it clearly in my

recognition of

the fact that an economical method of producing electrical vi-

brations of high frequency was the key for the solution

of a number most important problems in science and in-

dustry. Insignificant as

machines may seem to you,

they are nevertheless result of labors extending through a

number of years, and I can truthfully say that many times

the difficulties which I have encountered in my

to

perfect them have appeared to me so great as to almost

me of

to continue the work. When the ex-

nPr1m,"nnf'r has to spend

years of patient effort only

to

that a mere microscopical cavity or air bubble in

the essential

of this apparatus is fatal to the attainment

of result sought for by him; when he has to find that his

machine does not perform well because a wire he uses is a

quarter of an inch too long or too short; when he notes that

now a part his apparatus

in action will

colder

in an apparently inexplicable way, and next that the same

part will overheated, though to all

the condi-

tions are unchanged; when

observations

at every step and ordinary instruments and methods of mea-

surement are not available, then his progress is necessarily

slow and his energies are severely

Finally, I am glad

to say, I have triumphed over at least the chief obstacles,

and

any

stands now in the

way of obtaining electrical oscillations of frequencies up to a

few millions a second from ordinary supply circuits with

simple and fairly economical appliances. What this means I

not discuss. It will be judged by those who have

kept in touch with the development in this and allied fields.

These machines you see are a of the types I have

developed, and as they stand here they are chiefly intended

to replace the ordinary induction coil in its numerous uses.

34 TIlE STREAMS OF LENARD AND ROENTGEN
(/ {:

Fig. 1.-Method of transformation of electrical energy by oscillatory condenser discharges.

to broad

these transformers or electrical

oscillators, as they might most properly called, it is

pie enough has been advanced by me some five or

years ago. A condenser is charged from a suitable source

and is then in convenient way discharged through a cir-

cuit containing, as it

the primary of the trans-

former. first diagram, Fig. 1, illustrates a generator

a condenser C, for charging and discharging the

any kind

b adapted to

an intermittent

break in the dielectric. The circuit containing the high or

low tension

d through which the

dis-

charges being properly

extremely rapid electrical

vibrations which, so far we know are unattainable by any

other means, result; and these set up, by inductive action in

any neighboring circuits,

vibrations which give

to many curious phenomena. Having familiarized myself

with

at the time when some laws governing

were

not quite well understood, I have retained certain concep-

tions which I have then formed and which, though primi-

might stand even now in light of our

ad-

knowledge.

SECTION I

35

Fig. 2.-Mechanical analogy of electrical oscillator.
I have likened a condenser to a reservoir R into which by means of a pump P an incompressible fluid as water W is supplied through a feed pipe p, as illustrated in the second diagram, Fig 2, the fluid representing electricity, the pump the generator and the feed pipe the connecting wire. The reservoir has a movable bottom, held up by a spring S, and opens the ports 00 when the Iluid in the vessel has reached a certain height and the pressure has become sufficient to overcome the elastic force of the spring. To complete the model, adjustable weights w, a screw s for allowing the tension of the spring, and a valve v for regulating the Ilow of the fluid are provided. With the giving away of the bottom, the Iluid in the reservoir acquires velocity and consequently momentum, which results in an increased pressure against the bottom causing the latter to open wider, and more of the

36 THE STREAMS OF LENARD AND ROENTGEN

fluid rushes out than the

pipe can supply, whereupon

spring reasserts itself,

the ports, the

same process is repeated in more or rapid

This opening and closing of bottom may

the making and breaking of the conducting path, friction-

al resistance in mechanical system to the ohmic resis-

tance and, obviously, the

of the

masses to the

self-induction of the electric circuit. Now it evident that,

in order to

in action the mechanism without the em-

ployment of auxiliary means, the

rate of supply

through the must

to the

rate of dis-

charge through bottom; for, if it be otherwise, the ports

will simply remain open and no vibration will

place.

more

rate of supply equals the aver-

age rate of

the quicker will the bottom open and

close; and it is furthermore

from a consideration of

simple mechanical principles if the

supplied so

fast through the feed pipe that bottom vibrates as it

would of its own accord, then the amplitude of the vibration

will be largest, the

bottom the

the

amount fluid will be v ....,,""'....

through the ports. All these considerations hold good the

electric circuit, and in

with high frequency ma-

chines, which

were purposely magnified

with the view of rendering their observation more easy,

I have found that that condition is fulfilled when capaci-

ty, self-induction, frequency vibration bear a

relation, which observation I have

utilized in ad-

justment of inductive circuits. You will note that this condi-

tion

the rate supply and

most

portant in practice, especially when no

chanical means are employed for

the rupture of the

dielectric, is a distinct one and should not be confounded

with the condition determining the oscillatory character of

the discharge investigated long ago by Lord Kelvin.

next

in evolution of principle and

adaptation to practical uses was to

wi th the system

illustrated Fig. 1 a

coil as shown in

Fig. which modified the action in many now well

SECTION I

37

c
Fig. 3.-System mustrated in figure 1 with self-induction coil.

Fig. 4.-Coil wound to secure greatly increased

38 THE STREAMS OF LENARD AND ROENTGEN
,
(!
5.-Associating a secondary coil with it primary circuit coil.
~------------~[===lC~, ______________ ~
fi.~-S1J~t.~m adopted for "'''.'''Ull),; municipal circuits.

SECTION I

39

controller allowing condensers to discharge and successively.

Fig. S.-Arrangement of parts and circuits of a small oscillator.

40 THE STREAMS OF LENARD ANTI ROENI'OEN

understood ways. In a simplified

condenser, as a distinctive part

away with, necessary capacity

given to the coil

itsel f, and for thi s purpose the turns of the

wound as illustrated in Fig. 4 so as to

the

the

and

the largest possible amount ener-

gy.

I associated a secondary coil S with the primary

circuit P, as shown

enabling obtaining of

tension required.

in diagram

was adopted as sui table

munici-

circuits. Again, the self-explanatory diagram

typi-

cally illustrates a further improved disposition as

in

some of

machines with two or more

A modifi-

cation

plan with one continuous contact common to

two circuits, and independent interrupters for each

allows

adjustment of the phase of currents

the

which is practical advantage some

uses the apparatus. finally, in diagram Fig. 8 is shown

the exact arrangement the parts and circuits of one of

these small osciUators with a break similar to that

employed

with

coils. Although

majority of preceding arrangements have described

by me before, I thought it necessary to dwell on them here

in

to present clearly and comprehensively the subject.

A specific result of value the operation of Roentgen

bulbs is obtainable by the use of two

linked as

shown

7, or otherwise, or entirely independent

two separate primaries. Namely, in usual commercial

bulbs the vacuum gets higher when current is passed

through the

in a

direction and is lowered

when the direction the current is

This is a direct

COlnSC:QUlen(;e of some conditions which, as a rule, are

operation the usual apparatus; that is,

asymmetry of the opposite current impulses, the unequal

configuration or temperature of the two electrodes, or

causes which tend to

unequal the dissipation of

the energy from both electrodes. It should be stated,

though, that

a certain point,

the electrodes

begin to act as entirely independent, the vacuum continues to

increase no matter which way current is

through

primary. In the

illustrated in 7, or in its

SECTION I

41

Fig. 9.-Photograph of small oscillator diagrammatically shown in figure 8.
modifications referred to, the trouble attendant upon the operation of ordinary apparatus is practically done away with as the current though the primary is automatically reversed, and in this manner a tube which is first brought to the proper degree of exhaustion by means of one circuit can be worked for a long time without appreciable increase of vacuum or diminution of effectiveness.

42 THE STREAMS OF LENARD Ai'.'I) ROENTGEN

A photograph of one of these finished instruments,

Fig. especially

to be used in operation of

Roentgen bulbs, or in general as a laboratory appliance in

place of the ordinary induction coil,

an idea of ac-

arrangement of the parts. The condenser Fig. 8, is

contained in a box B upon which is mounted in front the

motor controlling the circuits, in this instance simply a

coil L actuating a spring s,

on of same. This

coil, designated as the charging coil, serves at the same time

to

the pressure of the source to any

desired

the condenser. This is an

practical

as it enables reduction the capacity of latter so

not be more a few

of that otherwise

"1"'""1(","" of energy. Besides, the

is the vibration and

shorter

be the high tension

. The "'1"'''-'''''.<1

P surrounding the secondary coil is formed

turns copper ribbon and mounted on top the

behind the charging coil, all connections being as short

as possible so as to reduce as much as it is practicable both

self-induction and resistance of the discharge circuit. On

the front side the box, 9, containing condenser,

are mounted the binding posts for connection with the

line, two

fuses, a reversing switch. addition,

two adjusting screws are provided raising and lowering

iron core within the

coil as a

means

for

within

current of

and regulating

the discharge of the secondary

cuit. The instrument rubber columns carrying the

rods, which are visible on top, dismounted, can

enclosed in a of x 9 x 6 inches inside measure.

The mode operation may

as follows: At

the start, the spring contacts cc,

being closed and the

practically short

a strong current passes

through the charging attracting the armature fastened to

spring and separating the contacts. Upon this, energy

stored the coil, assuming form of a high tension dis-

charge, rushes into the condenser charging the same to a

high potential. current through the coil now subsiding,

SEC110N I

43

the attraction

armature ceases, and the

spring reasserts

the contacts. With the

closing the

the condenser

the

primary or discharge

which are so

chosen that an extremely

vibration of

including

and primary coil

currents

high frequency thus obtained

induce corresponding currents of high tension in the sec-

ondary. Simultaneously, however, with the discharging of

the

current from

supply again

through the charging coil

is stored for

next charge of the condenser, this process

repeated as

as the spring

and closes the contacts.

Although the

contains all the essentials an

ordinary induction coil, it

seen that action is en-

different, and advantages of this new principle

over the old are so

as to hardly

any lengthy

comment. Merely to convey a true and more complete infor-

mation I

mention a few of the most important ones.

for instance, the economy. The instrument referred to

takes on a llO-volt direct-current circuit, according to load

and

from 5 to 30 watts. It

a powerful

stream of sparks 6

in

but be desired this

can easily doubled

increasmg energy

consumed; in fact, I have found it practicable to produce by

the use this principle

of 1 foot in length involving

no

expenditure of

than 10 watts. But in an

strument designed for a variety of uses, a departure must be

made from a design insuring the greatest

length. Of

the total energy consumed the apparatus, 80 percent

can be obtained

circuit. Owing to the small

consumed and

of

parts

instrument remain cool by long continued work-

ing with the

of contacts which, course, are

slightly heated. latter are subject to much less deteriora-

tion than is commonly case, as the condenser is small

and, moreover, the current from the same does not, like

an ordinary coil, pass simply through contacts and a few

connections, but has to traverse primary coil, this

the current and diminishing much the

effects.

44 THE STREAMS OF LENARD AND ROENTGEN

Consider next the advantages of the absence of fine

in the secondary coiL Owing to the rapidity of vibration of

currents, comparatively turns of

wire

the required pressure in the secondary circuit. illus-

trate this feature by a practical experiment I take a simple

paper cylinder, wound with only one layer ordinary

net wire,

the secondary In spite of there being

only a few

long

inches in length-

are obtained when the is inserted wi thin or brought near

to the discharge circuit of instrument. A secondary of

this form is simplest best suitable for the production of

sparks, but it is somewhat inconvenient to handle.

most advantageous features these instruments

however, in the quality of the effects produced, which are

the result the rapidity or suddenness of the discharges

tained. appreciate this

we only need consider that

a spark of, for instance, 6 inches in length, obtained with an

instrument giving half a million vibrations a second, in-

maximum pressures which, if produced with ordi-

nary methods, would

sparks many hundred

since the electrical force

to vibrate a certain quanti-

ty of electricity increases

rapidly; that is, with the

of the frequency of

Therefore,

as

obtainable cannot be

in any way

machines or ordinary induction coils.

Still another

of a more practical bearing I may il-

lustrate by lighting a vacuum tube from an instrument fur-

nishing currents of a frequency of much over half a million a

Sec:Ofllll. Although the tube has a volume of only

2 1/2

[cubic] inches, it emits more light than a tube 6 or 7 feet

long and 1

in diameter, such as I

shown on

other occasions, and that is a tube having 60 times the bulk

and

a proportionately larger amount of energy. So

small a tube as this shown could not at all be brought to this

luminosity by the use of the ordinary currents without soon

getting overheated, and no better test of the increased

ciency of the light production can had than producing

as a luminosity in a small tube without undue heating.

SECITONI

45

and advantageous feature of such an will be found its capability of being operated
as well as from direct-current municipal cirspecial object in view of enabling their being advantage on alternating circuits also, I have the physical constants in a few types to suit
'''''',~'''<' usually adopted here; that 60 or

IS nTn,'!1f'
the larger portion the flow of an core which is not on a research or in which there are general, estimate when a nrr..",o.. sipation or "''''''''rO'; agrees with the calculated

46 THE STREAMS OF LENARD AND ROENTGEN
...o.....
the condensers and coils, I have produced electromagnetic systems in which a slow vibration, once started, continues a minute or more, this indicating the absence of any serious friction loss. It is important to consider the preceding facts when dealing with standards and instruments of measure. A standard condenser prepared in the ordinary way of mica sheets and tinfoil, while indicating the correct value of capacity when used with a steady or slowly varying potential,

SECTION I

47

will have its measured capacity greatly increased when the

variation of potential

rapid. like man-

ner, an electrostatic voltmeter with its vanes immersed in

though a precious instrument

ordinary currents, is

practically useless in the measurement condenser

of frequencies of a hundred thousand a second,

11s indication

far too low.

the importance of subject, a words on insulating, which has been adopted by me

after

of experimentation, may of

One

form of apparatus as used by me is illustrated in diagram

Fig. 10. A is a

of withstanding great

which is connected to a pump E and reservoir

reservoir kept

by means the coiled

tank A is likewise provided wi th a coiled

which

steam or cold water may

condenser is build up of insulating and conduct-

in any

way, several layers of very thin

being together so as to avoid defects which may

from

holes or punctures. the same reason, it

is

to mix the sheets when received from

factory, as a great number of them may injured at the

same place. The

been

by the appli-

cation moderate electrical pressure as that of a supply cir-

cuit 220 volts, is placed a

vessel B. A pipe D,

reaching to bottom of this

may provided,

through which the insulation, when liquefied the

may flow in, but this is of containing the condenser

importance. vessel B

next placed in the

A,

and the top of the latter bolted down, stearn is then passed

through the

pipe C the insulating mass is kept at

[proper] temperature which is a little above the melting

point of the compound regulating the stearn supply. The

pump is now connected with the

by opening the nrA....."r

valves, and a vacuum about inches or slightly more is

established. When the melted compound has thoroughly

permeated the interstices of the condenser, steam is then shut

cold water passed through the coil C. The process of

slow cooling being

far

the connections of

48 THE STREAMS OF LENARD AND ROENTGEN
the pump are reversed and air is forced into the tank A with the result of compressing strongly the fluid insulation and forcing it into all interstices. The pressure is preferably maintained until the mass is solidified. The application of the pressure is not only of great advantage because the insulation is forced into the interstices and prevented from shrinking away when cooling, but, in addition, any small gas bubble, which might remain in the condenser and would otherwise at ordinary atmospheric or smaller pressure be fatal to the instrument, is strongly compressed and the danger considerably lessened. The mass in the tank A being solidified, stearn is again turned on the pipe C for a few minutes in order to soften the insulation on the periphery and allow the
/
/
Fig. It.-High potential coil system having terminals at centers.
vessel B to be lifted out of the tank, whereupon the con-
denser is taken out of the vessel and the superfluous insulation cut off. In the same manner, primary and secondary coils are treated. As insulating material, I have found best to use a mixture of beeswax and paraffin of low melting point, about half of each being taken. This gives a tough mass which [but slightly] shrinks away from the metal upon cooling. Condensers and coils manufactured in this manner will withstand incredible pressures. Very often in adjusting the primary discharge circuit, it may happen that sparks of 3/8 or 112 inch dart across the condenser terminals, and yet it will

SECTION I

49

'L_.. not break down, although the ....'..

is no more than a

few thousandth of an inch in ..u,"~,,~u~ I have been unable

to detect any increase of

whatever in the con-

denser after long working.

to withstand the effect of

with

instruments,

to build them on the gener-

shows two flat

are connected with their nrr\nl'>r direction so as to

the terminals of

the two wooden

are wound.

thin fiber

to

solidity and

'''''-'''''''''.... wax to fill the hollow insulating process

centers of spools are fastened

bushings to which the free ends of the

are connected and into which can be

ss.

are fastened to the end of

rubber rr, through which pass flex-

ible wires ww,

heavily insulated with gutta-percha,

which serve to connect secondary high potential ends to

the

on the top of the instrument

(Fig. 9), It

not to insulate the wires ww with

soft rubber,

kind of insulation is soon destroyed by

at their surface in consequence of the

even if the rubber be very thick.

insulation between the superimposed

is practically determined from an

difference of potential between

_"'''.__ '.] I have used heavily insulated wires

with from two to four braids, but presently I am

ordinary

wire which, in manufacturing the coil,

wound

with a string of a thickness equal to

of the

is a convenient mode of insulating, not

prepared wire and secures

re-

of the secondary circuit, or common

is connected to ground, or so the mains,

50 THE STREAMS OF LENARD AND ROENTGEN

and this generally through primary discharge

The

small contact plate, or spring serves to establish con-

upon the secondary

being

the pri-

mary coil. The length of

the secondary coils is so

determined that it is somewhat less or equal to a quarter of

the

of the

disturbance produced

in the

course, on the

es-

propagation of

through this circuit. It is obviously

that the

length of the secondary circuit is made to approximate more

or less a quarter of the wavelength, according to how much

allowance is made for the capacity of the circuit under nor-

working conditions. the ordinary uses of the instru-

as [a] laboratory

chiefly for production

effects

tension discharges, little a1-

is generally

capacity the terminals~

but if the apparatus is

for instance generating a

quantity of streamers between plates of

surface,

charging

from the

or [other]

uses, then

of the

is made

much smaller, and advantageously an even fraction of a

of that

which is

without any

for capacity

than that

by the coil.

Finally, if secondary currents of

low tension

are desired, the coil is constructed

one

spool and of only layers, all in

proXImIty to

primary so as to

the mutual induction coefficient

reduce the resonant rise of potential as much as possi-

ble. The closure of the magnetic circuit oxygen at ordi-

or high

while of little

with low

currents, is a remarkable

wi th currents

these unusually

when

conditions are

the occurrence resonant phe-

nomena, and I am anticipating practical uses of oxygen in

connection.

A secondary coil constructed in manner illustrated

11 has many important advantages, the chief ones being

safety in handling and the facility it affords for obtaining

ootentlals far

those producible if the ordinary

of construction are followed. In

to convey an

SECTION I

51

of the pressures obtainable even with so small an instrument

as one described, a photograph the same action

with two loops of cotton-covered wire attached to the dis-

charge rods, is added (Fig.

outer wire loop was in

the experiment only

in diameter to enable it being

properly shown in the print, but it could have been much

larger since two

parallel wires feet long may be

stretched the secondary terminals of instrument

practically the whole space between them, 4 inches wide, is

seen in dark covered with fine luminous streamers.

is a surface of 5 square feet, and yet the energy taken from

the supply circuit during the performance is

35

watts. To produce with an ordinary transformer such a

quantity of these streamers, which may be

for

manufacture of ozone or similar purposes, would require a

considerably

amount of

and a more costly ap-

paratus.

These extreme

of potential obtainable by the

use the principle here involved are the result of the enor-

mous suddenness or rate of change the primary current

impulses. In the ordinary method of

the strength of

the primary current, either by alternating same or break-

the conducting path, we are limited to the comparatively

insignificant rate of

producible by means of a high

frequency

or rapid

but by use of the

condenser discharges is practically no limit to the sud-

denness the impulses, and any potentials and spark

lengths desired can be readily obtained.

instance,

I have been able to produce, by applying the principle in a

peculiar manner, immense

the theoreti-

cal maximum value of which can measured only in many

millions volts, causing showers of continuous streams

thundering

to dart out into

to a distance

of 8 or 9 feet from an insulated wire, which behave some-

times like veritable lightening bolts and have afforded to the

few who

witnessed them during last two or three

years in my laboratory a

not easily forgotten. Nor

is it at all difficult to increase, a

hall or open space,

52 THE STREAMS OF LENARD AND ROENTGEN
Fig. 12.-Photograph of coil system illustrated in figure 11 in action. Luminous streams cover an area of 5 square feel

SECTION I

53

many times the potential and sparking distance by the employment of such means and methods,

Although in

oscillators great suddenness of

change the strength of currents depends chiefly on the

electrical constants of the

some advantages of minor

but practical importance may secured by a proper con-

struction of the devices used as convenient, though not in-

dispensable, accessories of system for the purpose of ar-

bitrarily making and breaking circuits. Accordingly, I have devoted considerable time to their study and perfec-

tion, and in connection with the typical arrangements of the

circuits illustrated in

1, 4, and 5, I have dwelt in my

earlier

on this subject on a variety of such circuit

temlpters in vacuum, air, other fluids at low or great

pressures.

It been known long ago,

the investigations

Poggendorff, that, when the vibrator or break of an induc-

tion was enclosed in an exhausted vessel, interrup-

tion of the currents was

suddenness,

the vacuous space acting in a certain measure like a con-

denser, connected, as usual, around the break. Myexperi-

ments wi th several kinds of such circui t breakers have led

me to

that vacuous space is not exactly

equivalent a

but

of an

the

rrp!l""'rI suddenness being simply due to the rapid carrying

away of the volatilized material forming the arc and, there-

fore, dependent on the velocity with which disintegrated

matter is

away and also on amount of latter.

Thus, with very hard platinum-iridium contacts small

currents, there is little difference; but, with soft platinum

points and heavy currents, influence of the vacuum is

well noticeable, while, with mercury or in

easily

volatilizable conductors, the difference is very great. The

of the exhausted

is also of some consequence,

break gaining suddenness when the

is larger.

Looking at Poggendorff's observations in this light, it ap-

peared clear to me that only a small velocity of the particles

composing arc can be obtained

the effective

at least with low frequency impulses

5+

THE STREAMS OF LENARD Al\TD ROENTGEN

mechanical means, and with currents of limited strength which can be passed through the contacts without quickly destroying them, is necessarily only a minute fraction of the atmosphere being besides, very materially reduced by the oppositely acting attraction of the parallel-current elements of the arc. Pursuing further this train of reasoning, it seemed likewise evident that, if an insulating fluid be forced mechanically between the contact points with such velocity that the particles composing the arc were carried away quicker than it was possible with a small pressure producible in the gaseous matter in vacuum, the suddenness of disruption would be increased. This conclusion was borne out by my experiments in which I found that a fluid insulator, such as oil or alcohol, forced through the gap with even moderate velocity, increased very greatly the maximum rate of change of the primary current, and the length of secondary wire necessary for a certain spark length was in some instances reduced to 25 percent of that usually required. The length of the secondary was still further reduced by the use of insulating fluids under great pressure. As regards the suddenness of the current impulse following the closing of the contacts, the introduction of an insulating space or film of greater dielectric strength than that of the air at ordinary pressure, though producing a distinct effect, is of small consequence when the interrupter in 1tS operation actually breaks the arc, since the electromotive force of a battery or municipal supply circuit is generally insufficient to break down an insulating film of even so small a thickness as 0.001 inch.

The continued effort to perfect the various automatic
contrivances for controlling the supply current has clearly brought out their mechanical limitations, and the idea of utilizing the discharges of the condenser as a means for producing, independently of such mechanical devices, the sudden variations of the current which are needed for many pur-
poses in the arts, appears evermore a happy and timely solution. In this novel process, a function of only minor importance is assigned to the mechanical means; namely, that of merely starting periodically the vibration of the electromagnetic system, and they have no other requirements to fulfill beyond those of reliability in operation and durability, features which are left to the skill of the mechanic and which,

SECTION I

55

in a fair measure, it was not difficult to attain in a number of types.
Considering, then, that the rate of change of the discharge or primary current in these instruments is made to depend chiefly on the physical constants of the circuit through which the condenser discharges, it is evidently of utmost importance to construct properly the latter circuit, and in the
QallOrlS which were carried on with this object in view, several noteworthy observations have been made.

First of all, one draws the obvious conclusion that, inas-

much as the primary coil in a transformer of this kind con-

usually very few turns of copper

of inappre-

ciable resistances, the insulation between the turns should

not require much care. practical

soon con-

vinces him of his error, for, very often it happens that,

owing to an exceptional resonant

difference of

tential between adjacent turns becomes so great as to rupture

even a good ordinary insulation. this reason, it was

found necessary to treat the primary coils likewise in the

manner described, thus securing the additional advantage of

which

from the expansion of the metal

sheets and thickening of the insulating layers during the

heating in vacuum and subsequent contraction of the metal

in cooling to the normal temperature after the insulation has solidified.

the experimenter is surprised when realizing the importance the proper adjustment of the length of the pri-

mary coil

He is naturally prepared to

find that,

the discharge circuit is of small length, the

introduction in this circuit of a small inductance or

tional

would produce an appreciable difference in

result obtained as, for instance, in the spark length of the

secondary coil. But he certainly does not expect to observe

that sometimes as little as 1/4 inch conductor more or less

would be of a telling effect. To illustrate: It is quite easy to

produce with this kind of apparatus a spark of

feet in

length, and by merely taking off or adding to the primary

56 THE STREAMS OF LENARD Al\ro ROENTGEN

wire so

the spark length to one

this kind impress the experimenter

with the importance the

adjustment

circuits

accurate determination of

constants.

is forcibly

to the

of reducing as much as

it is practicable self-induction and resistance

dis-

circuit, former with object of

the

quickest possible vibration, the

chiefly for reasons of

necessity bringing

down to the minimum

resistance all con-

necting wires. A

discharge

a small

instrument,

as the one

should

five percent of inactive conductor; its

should

negligible, the self-induction should be not more than

a few

centimeters)'" 1 I

found it

Impera-

to use thin

the pri-

mary coils, with these an

is the most

curious of

been made. It occurs, namely, that, under

certain conditions, the primary coil gets

cooler

by continued working. For a long time this

appeared

doubtful, but finally it was positively ascertained and as-

cribed to an

effect,

to which

heat is of the COI1denS(~r.

to the tinfoil

It might not appear quite

at first why the primary

discharge

is so

to variations of length, for a

circuit of length

connected to condenser

and,

that

between

capacity

and

is

as to satisfy

laid

down by

KelVin, oscillatory discharge will take

But it must remembered that the velocity of propagation

of the disturbance in the circuit depends on

quantities,

and that best result is

when the velocity is

that a

wave is

with a single node which is

located

but not always, at a point of discharge

circuit or conductor equidistant from the opposite '"''VA......'"''

coatings. Under such

the maximum

pressure at the terminals

is obtained.

units. a few tenths microhenrys.

SECTION I

57

possible when the speed of the

is such that this

exactly in the time

one vibration. Now, since

the circuit very small,

.........'V110 of the length may often pro-

performance of the appara-

tus.

course, should not be construed as

generally al.l~/H.....aUl""'.

only to such cases in

which

started by one

operation of the

not die out before the

succeeding operation the controller.

may be made

clear by a mechanical

Suppose a weighted spring

is clamped in a

blow is struck which sets

the spring vibrating.

vibrations die out and let anoth-

er blow be delivered.

will vibrate again as be-

fore, and it matters little

weight is attached to the

spring, what the elasticity

or, in general, what its

period of vibration, and at

the blows are de-

livered, process blows into the p",,.rO'u

of the energy of the vibrations will effected with

equal economy, except for ".....-VH....""l causes, immaterial for

the present consideration.

so is it with the

magnetiC system, and in

of

practical adaptation of the

ments described, I have

nary or electrolytic, of very

them to discharge at

a primary circui t

thus producing current

reach, at least theoretically,

100,000 amperes. A high maximum rate

mary current was thus produci ble, but,

erage rate of change was still small. '-"vue....."'"

mechanical analogue before

at once derived. Looking upon the

pliance for converting energy, both

and output

mand that the vibration of the spring should nprClIH

as possible and that the blows should be

is practicable. To satisfy this twofold

58 TIIE STREAMS OF LENARD AND ROENTGEN

must of

be delivered

the spring is still vibrat-

ing, and now it becomes most important to properly time the

blows. Similarly again, the electromagnetic system, the

controller must operate at definite intervals of

to secure most

vibration with the

supply of energy. In the construction of pm:;tlcal

ments, number of the fundamental current impulses is

arbitrarily adopted; the condenser,

prepared by a spe-

process, cannot be adjusted

great inconve-

and

and to a

extent also the turns of

the primary coil are likewise determined beforehand from

practical considerations. Furthermore, it is desirable,

reasons of economy, not to resort to an otherwise conve-

nient method of adjustment, which would be to

a vari-

able self-induction in

with primary

These

conditions

more difficult the exact adjustment of the

various quantities, and I have sometimes found it of advan-

tage to adopt one or other plan such as will readily suggest

themselves. For example, I have used an additional coil

wound upon the primary and connected in parallel to the

same, or I have completed the adjustments by determining

properly the self-induction and capacity of the secondary

coiL

In order to facilitate the observation and to enable

the exact determination of the oscillations of electromagnetic

systems as well as of vibrations or revolutions of me-

chanical

such as circuit controllers used con-

''''''''''VJ'', it was recognized as indispensable, in the course of

investigations, to construct a proper apparatus for such

purposes. I determined from outset to

myself

what is known as visual synchronism. In this scheme, usu-

ally a or cylinder with marks or divisions, which is ro-

tated with uniform

is illuminated by a periodically

varying or intermittent source of light, divisions appear-

stationary space when revolutions of the disk are

synchronous with the

in intensity or intermittence

of the light-giving source. The virtue of such a method

evidently resides in uniformity the velocity of rotation

or eventually in the

of period of the vibration

produced. Having been

confronted with problem

SECIIONI

59

of rotating a body with rigorously uniform velocity, which

is required many instances, or with the

problem

producing a vibration of constant period, I have devoted

some

to the study of this subject, in the course

of time several solutions, more or practical satisfac-

tory, have presented themselves.

for instance, was to

by means of

nrp·"",,,,·t1 air or steam, the vibration of a freely movable

plunger to which was rigidly connected a coil or core of an

electric generator.

the

motion of the

plunger, alternating currents were generated which were

passed through a

or through primary of

a transformer, in which case the secondary coil of latter

was joined to the terminals of the condenser. Care being

taken that the air or steam pressure was applied only during

a short interval of

when plunger was passing

through the center of

and the oscillations of the

system, composed of

and

generating coil, being properly determined so that funda-

mental resonance took place, it was found that, under such

conditions, the

governed the

of plunger; the

applied fluid

pressure, while capable of producing

in the ampli-

tude, were

very wide

without any appreciable

on period of vibration of mechanical system,

the currents generated

therefore of rigorously constant

period.

currents thus obtained were then utilized in

a number of ways to produce uniform rotation.

Another way to

the same resul t and in a more prac-

tical manner was to

currents of differing phase by a

steam engine of special design, which the reciprocating

motion of the work performing plungers and attached mag-

netic cores or coils was controlled by a freely oscillating

valve, the period of which was maintained constant by

mechanical means or by the use an electromagnetic

tern, similarly as before. A synchronous alternating motor

operated by the two or three phase currents thus generated

rotated with so uniform a velocity as to drive the wheel

work of a

with fair

60 THE STREAMS OF LENARD AND ROENTGEN

Still other solutions of the problems

to I may

mention which, though satisfactory, have proved some-

times convenient and sufficient for many purposes.

a direct-current motor

laminated

or

without any iron, was connected in series with a condenser

through a commutator or interrupter fastened on the shaft

a light [weight] armature. This device was so constructed

that it alternately closed and opened the terminals of con-

as usual in the instruments before described. The

condenser terminals being closed, a strong current impulse

through the motor, and upon the terminals being

opened the discharge current high tension rushed into the

But the

duration of both of

suc-

ceeding current impulses, and consequently all which

passed through the motor, were made chiefly dependent on

the self-induction of motor coils on the capacity of

the condenser and were, therefore, with certain limits of

variation the applied

little dependent

on latter, and consequently a motor with a negligible

tion

operated in this manner, turned with nearly uni-

form velocity. The

was the more

constant

controlling influence of electromagnetic sys-

tem which, of course, was most complete when the

number current impulses, the capacity, and self-induction

were so adjusted

fundamental resonance was

~u,"'~. As before

in most these novel instruments

described, such adjustments are observed and, whether pro-

vided with rotating interrupters or circuit-controlling

springs, they partake more or less of virtue

pre-

ceding principle. For this reason, the contact springs in

these instruments not fall into harmonics, as they

do ordinary induction coils

from supply circuits

where physical constants are generally such that similar

adjustments are impracticable.

It should

that,

a long time, it was

known a

motor, driven with currents

terrupted at regular intervals,

a marked tendency to

maintaining a constant speed; but by introduction

a condenser in the circuit and the careful adjustment

quantities, this

is very much

and for

many purposes a

uniform

SECTION I

61

obtained in this manner. Instead of using interrupted cur-

rents for operating the motor, it is practicable to rotate a sep-

arate coil, wound

on same or on a second arma-

and to pass alternating currents generated in this

coil through the condenser. It is important for the attainment

a satisfactory result in such cases to determine the con-

stants so that the amount of

stored in the COlna(~nSler

should as large as possible.

While a number of such arrangements were readily avail-

able, it was found, nevertheless, that they were inadequate

to the many different requirements of the laboratory, and ac-

cordingly an instrument was devised which is illustrated in

13 abo It proved itself to so necessary and valu-

able an implement in experimental investigations that

scription here may afford

information. cut is in-

."''',...v .... to show a substantial and carefully constructed clock mechanism with the usual escapement e, gearwheels ggg,

and a I-second pendulum A small shaft s, carrying a disk

of

diameter, was geared to the clockwork through

a pinion p of a proper number of teeth, as to give to the

shaft a velocity best suitable for observations. Now, in

to rotate the with a uniform velocity, some diffi-

culties, well known to clockmakers, had to be overcome.

is due to the fact that rotation of

shaft s, being controlled by the escapement e, which, at

ular intervals, retards train of wheels ggg, is not effected

with uniform but periodically varying velocity, which may

all values from zero to a maximum, dependent on the

driving weight W. Owing to this circumstance, when such a

disk D of large diameter is rigidly geared to any kind

clockwork, it exerts, by reason of the

momentum

which it necessarily acquires, a strong reaction upon the

pendulum, altering the

of the same more or less, ac-

cording to the momentum it

This difficulty is

known to

even in cases in which the step by step

movement is practically done away with, as, for

in

with centrifugal governors, or circular pendu-

which slow oscillations are produced the reac-

the moving mass upon the regulating Ul...,.......U.1U.:>Ul

R)
~
!
rfJ
o
'Tl
hz 1
~ ~
~
I
t:f
Fig. 13.-Special instrument to exactly determine wavelength and phase.

SECTION I

63

have proposed an

tween the body driven and the

[do] away radically with the difficulty.

when, in an attempt to overcome

step-by-step movement, a

whereby the periods of rest are

the inf1uence of the momentum of the

body upon the

nprl£Vl of the pendulum, the result aimed at is but imperfect-

and, besides, such an apparatus is suitable

observation. Namely, it will be recognized as desirable

for a number of reasons the disk D should be rotated

normally either once or twice a

to

whether a 1- or lA-second pendulum is used. This being the

case, the experimenter can render himself easily an account

of the constancy of the speed by observing a mark m on the

and noting that it occupies a fixed position in

rel-

to that of the pendulum, in a

phase

tion.

the computation the vibrations is ren-

dered

more convenient under such conditions.

problem, clearly put, was then to rotate a

as

the disk or other

with any desired but uniform ve-

locity in a such the

of vibration of pen-

dulum was not

affected, even though the

rotated

possessed considerable momentum. entirely satisfactory

solution of this problem was arrived at in the following

manner. On end of the shaft s, Fig. b, was fastened
a light metal piece f in the shape a cross, carrying on two

its opposite sides pivoted pawls PI and on the other

two light springs rj which

the pawls gently

against the periphery of a washer w, which was provided

with many very fine teeth or serrations cut

SImI-

larly to

of escapement

ranged to turn very

tened the di sk D.

edges to fit in the

w, and

means disk could rotate freely on the shaft s in the

tion indicated the arrows, but rotation the

direction was prevented by the

64 THE STREAMS OF LENARD AND ROENTGEN

apparatus now be at once un-

escapement wheel e was

by unscrewing the thumb screw t and shifting the sleeve S

on rocking support. The pendulum was next started

when the escapement wheel had attained the normal ve-

locity, the sleeve S was slipped back quickly

fastened-control

escapement

being thus

to pendulum.

work and the shaft snow

rn"'"""" with periodically varying

but the disk D

to move uniformly, the pawls Pl P2 slipping on

the periphery of the washer w during periods when

of the

the pendulum.

to the very

but unavoidable

in

and bearings, the

disk would slowly diminish and fall below

maximum velocity which the shaft s was capable of impart-

ing to then the pawls would give it a

impulse,

in this manner the disk was kept constantly at the maximum

velocity. By each

of the pendulum, the disk would

thus

one

its

on the

energy

to it by

the succeeding

This amount of energy

of course, on

of the shaft s during the period when the '-'0...,..AtJ"'-

ment

was free, since this velocity was determined

by the driving weight, the speed of the

of the disk

could

within

limits by

the weight.

It will observed

would rotate

faster than

weight so that

the pendulum.

infl uence of

period the pendulum is

course, could not be 'UL<:UU\:;U

with

s, even if a

used, as

suggested.

uniformity rotation se-

cured in this way leaves, for all practical

at least,

nothing to desired. The apparatus might

been im-

proved by supporting the

on an independent bearing

SECTION I

65

and, perhaps,

by

it horizontally in a jeweled

support. But the friction

was very small, since, by

arresting shaft s suddenly, disk would generally

rotate something like 100 times or more before stopping,

and such improvements were thought unnecessary. The ver-

tical position was, however, chosen

it was much

more

for purposes of observation. In

to re-

duce weight of disk as much as possible, a

consisting of a circular rim with narrow spokes, was

cut out of thin aluminum sheet, and black paper glued on the

frame-all marks and divisions of former being, of

course, white. I found it convenient to draw concentric cir-

cles a number of marks such that all vibrations within

the

of apparatus could read In addition,

a segmental piece hard rubber N, supported on a T

and properly marked, was used to read fractions or, respec-

tively, take corrections for any irregularity the rotation

during a prolonged period of

the disk was placed

a vacuum tube or, in place, an adjustable spark gap I,

which was

to the secondary of a small trans-

former, the primary which was positively controlled by

the mechanical or electromagnetic system the vibrations of

which were to determined. In preparing a spring the

desired period vibration for one of the instruments

scribed, for

the spring was provisorily mounted on

the instrument and the latter put in operation. The disk, in-

termittently illuminated by the discharges of the secondary

was released from the pendulum and rotated until syn-

chronism was attained, the revolutions being computed by

observing the white mark m. The constants of the spring

were modified a simple calculation from the first

result, and in the

trial, as a the vibration was so

as to enable use of the escapement, the adjustment

being completed, generally by altering the weight of the

hammer on the spring until marks on disk, by the

normal speed rotation, appeared stationary in space.

66 THE STREAMS OF LENARD Al'-'D ROENTGEN

The apparatus described in

convenient and saving in a

many lines of

mentation. By means of the same, it is practicable to rotate

a body of

weight with uniform and adjustable

velocity, and it

itself to the operation of circuit con-

trollers, curve

and all kinds of such devices. It will

found most

in tracing current or electromotive-

curves

of

will afford mate-

help in

a

most valuable use in the

tions is, perhaps, the purpose determining

angular velocities of dynamos, particularly of

Among the various quantities which, in alternate-current ex-

practice, one to determine

fre-

quently, there are some, which even a laboratory or shop

in the midst of disturbances a or

can

ascertained with sufficient precision, while there are others

which can be only approximated, particularly if, as is very

often the case, practical methods of measure must resort-

ed to. So, for example, the close measurement of resistances

no

nor does that currents

tive forces, although the

exactitude is ne(:es~;;an

smaller; but in determining

one is

to make a

considerable error, still a

one in measuring induc-

tances, and probably the

estimating

In many

such crude

as speed counters or

tachometers are still resorted

the experimenter is dis-

appointed to

that

of long and

painstaking tests is impaired

to deter-

mine exactly frequency.

often too, latter is the

and most important quanti-

ty. In view of these facts, a description of the method adopt-

ed by me

determination angular

may be

some

The

commonly

are illustrated diagrammati-

cally in

a and b. On shaft S,

a, of the

generator fastened a commutator or

controller C,

provided with any suitable number of

eight being

SECTION I

67

~

til
~.;.:.:.

<1/

E

~

b
.Stil

.....

0

;::

0

~

;<:I:I

~ ....
<'

s·S

<1/

-;til

Q..
.§
.....
0

"C

0

tl

':5

::<;1;/

I
~....

....o.....il

shown in this instance. Four of these, 1, 3, 5, and 7 serve
to establish the connections of the circuits, while the intermediate ones, 2, 4, 6, and 8 are entirely insulated, idle seg-
ments. Assuming the generator to be an alternate-current machine, the terminals tl t2 of the armature winding, or of any desired coil or part of the same, are led through the hollow shaft, as may be the case, and connected to the diametri-
cally opposite segments 3 and 7, while the segments situated at right angles, that is 1 and 5, are connected together through a wire w of inappreciable resistance. Two brushes bl b2 , supported in an ordinary holder allowing their being shifted in any position, are arranged to bear upon the periphery of the controller C. These brushes are connected to a

68 THE STREAMS OF LENARD AND ROENTGEN

circuit primary coil p, induction and denser.

c of proper capacity and a turns of very small selfin series with the con-

The operation of

fore referred to. When,

brushes bl bz are 1 and 3, the condenser is

adjusted at will by shifting

retains a certain charge until

upon the connected

latory discharge

result of inducing

s, which momentarily

I placed in proximity

uniform velocity, as before

the circuit controller, the

tact wi th the

J

peated, at

complete

a definite number of impulses

uum tube or spark

be only two'

but any greater number be

the number of the segments and

manner. It should be stated that current

pass into the condenser whenever the

those segments which are connected to

dinarily produce no appreciable

This might be the case if the

very large and would then be at once

justment of the circuit through which

charges is, of course, preferable but not

sary.

When it is inconvenient to use armature

lustrated in Fig. 14 a, then the controller Cis

two sliding rings r1 rz, Fig. 14 b, bear two additional brushes b3 b4• nected to a direct-current source as

which are

preferably through a self-induction

SECTION I

69

to

to a higher potentiaL The

'1 '2

merel y

to the segments 1 and 3 current charg-

ing the condenser, otherwise nothing

be changed on

the 1"1.0," "'I'>

The marks or divisions on periphery the disk D

are suitably

so that by normal speed of the genera-

appear stationary in space,

being the case, the

may be at once and easily computed from the number

segments on the controller and that of divisions on the

disk and from the speed of the iatteJ: The frequency of

dynamo currents is then

by taking into consideration

the

of

availing himself of this method, the experimenter can

get the accurate value for angular velocity, no matter

how much the speed of the dynamo may vary, if he only

the precaution to

his readings for electromotive

etc" at instant the

on the disk are

stationary. Should the

consume more time, It IS easy

to take the

for any variation by simply observing,

with

to a fixed line on rubber piece N, the

number of divisions which are to added or uo;:;\~u\,.u;;;u

from, the

of disk.

Section I Addendum

TELEGRt\PHY

METHODS;

IN ELECTRICAL OSCILLATORS;

VACUUM BULBS.

lecture was not completed

The

and

",;"},,",e:u. in the

lec-

ture on subject of

telegraphy re-

methods, an extension his presenta-

tion on novel high

measurement

were considered

too revealing

in terms of patent applications in progress. The

following Addendum section is derived from

Section IX, IIArrangements for receiving,"

Nikola Tesla On His Work With Alternating

and is believed to summarize his re-

on this

"The

[of the instrument shown in Section I,

Fig. 13 cut] was intended to produce an absolutely constant

rotation so that certain intervals of could be definitely

fixed, and in

to these

of time I could ana-

lyze the waves... The bottom of

[Fig.

shows vacuum

designed for

currents.

They were

secondary

transformer and

illuminated the

I used, for'

two vibrations of

different

then there was a

and I would

notice, as this rotated, the marked travel one way

or the other. When

synchronism was obtained,

lines appeared stationary.

"I am now showing [Fig. 15, top] a [drawing of a]

for telephonic and telegraphic

I used in my

laboratory on

[left! is a transmitter

... , [below] is an inductance which is bridged by a

such as by speaking into it, or

it by hand

or otherwise, variations in the intensity of the waves are

produced.

72

THE STREAMS OF LENARD AND ROENTGEN

fig. 15. Devices for receiving.
"On the receiver side [right] I have my antenna and selfinductance coil connected to the ground, and in the secondary I have a wire which is under a tension. Another wire, likewise under tension, controls two microphonic contacts or carbons. The tension of this wire is adjustable, and as I will show in another drawing, I can regulate the pressure of the contacts so that a certain current from a battery, here, will flow through this primary coil.
"When the transmitted oscillations are controlled and produce corresponding variations in the intensity of the received effects, then the current generated in [the secondary of the receiver] heats that wire more or less and the alternate heating and cooling of the latter results in periodic expansions and contractions vary[ing] the microphonic pressure of the contacts in obedience to the changes produced in the transmitter. In the secondary [of the transformer], I have a telephone [receiver] specially wound to reproduce the speech... "
"My transmitter was on Houston Street and I would take the receiver with me. For instance, I would take a few toy balloons, go on the roof, and then put my box there with the instruments and listen to the signals.

SECTION I - ADDENDUM

73

"This [Fig. 15, bottom] is another [drawing of a] device which I also used with success, but not telephonic. It operated on the principle of the Reis air thermometer ... [I]n the bulb is a resistance wire which is heated and cooled, owing to the fluctuations of the received currents. The attendant expansions and contractions of the air operate a little mercury column, pushing it back and forth. Curiously enough, for receiving telegraphic signals, this crude instrument was certainly good, but of course it was not suited for telephonic reception.

"That[shown in Fig. 16] ... illustrates a way of producing audible notes by reaction of the received impulses upon a magnetic field . [At upper left] is a transmitter, diagrammatically represented, with an arrangement for varying the intensity of the waves emitted, and on the receiver side I have, as you see, a grounded antenna. [The] secondary [has a conductor under tension in] a very powerful magnetic field, and [the reaction of] this conductor, traversed by the received currents in the field, causes the conductor to emit audible notes.

o
__._.__ .(~J
~'--I:=~_~_J=t---Q
Me)

Fig. 16. Other Ways of receiving.
"I [have] several magnets of various forms, like this [Fig. 16, center], and employed a cord in the field, which, when the current traversed it, vibrated and established a contact. Or, I [use] a small coil... through which the current

74 TIIE STREAMS OF LENARD AND ROENTGEN
was passed, and which by its vibrations produced the signal, an audible note, or anything else ... [I]n my writings ... I had already shown the reaction of the high frequency and low frequency currents on magnetic fields, and had specified the frequencies within which one has to keep in order to receive efficiently audible notes."
In addition to the electrical oscillator unit shown in Fig. 9, Section I, Tesla also exhibited two other units. The first is shown in Fig. 17 which was covered by a patent applied for nine months earlier.49 A second is shown in Fig. 18 an advance look at a form of oscillator utilizing one of a series of eight hermetically-sealed, mercury circuit controllers for which patents were applied beginning the following two months. This unit was covered by a patent applied for eight months later.5O

Fig. 17

Fig. 18

These units were described by Tesla the following way years later as presented for the lecture.
49 U.S. Patent No. 568,179 of Sept. 22, 1896, "Method and Apparatus for Producing Currents of High Frequency," application filed July 6, 1896.
50 U.S. Patent No. 609,245 of Aug. 16, 1898, "Electrical-Circuit Controller," application filed Dec. 2, 1897

SECTION I ADDENDUM

75

"[The unit in 17]

a

oscillator ...

tended for

production Roentgen

rays, and scientific research in general. It comprises a box

containing two condensers of the same capacity on which

are supported the charging coil and transformer.

auto-

matic circuit controller, hand switch and connecting posts

are mounted on the front plate of the inductance spool as is

also one of the contact springs. The

box is

equipped with three terminals, the two external ones serving

merely for connection while middle one carries a contact

bar WIth a screw for regulating the interval during which the

circuit is closed. The vibrating spring itself, the func-

tion of which is to cause periodic interruptions, can be ad-

justed in strength as well as distance from the core

the center the charging coil by screws visible on the

top plate so that any desired conditions of mechanical con-

trol might be secured. The primary coil of the transformer is

of copper sheet and taps are made at suitable points for the

purpose of varying, at will, the number of turns. The induc-

tance coil is wound two

to adapt the instrument

both to llO and volt circuit"> and

secondaries

were provided to

various wavelengths

prima-

ry. The output was approximately 500 watts with damped

waves

50,000 cycles per second. short periods of

time undamped oscillations were produced in screwing the

vibrating spring tight against the iron core and separating the

contacts by the adjustmg screw which

performed the

function of a key.

"[The unit in Fig. illustrates a transformer with a ro-

tary break.

are two condensers of the same capacity in

the box which can connected in

or multiple. The

charging inductarlCes are in the form of two long spools

upon which are supported secondary

A small

direct-current motor, the speed of which can be

with-

wide limits, is employed to drive a specially

make and

In other

the oscillator is like the

one illustrated [at left] and operation will

derstood from the

This transformer was

m

my wireless experiments fre~uently for lighting

laboratory by my vacuum

" I

51

"Electrical

" Electrical

259-260, 276, 276.

76 TIlE STREAMS OF LENARD AND ROENTGEN
"[I now show on the wall of this Academy drawings of] a great variety of bulbs I used. Every one that you see was built, not in one, but in several forms ... Among these bulbs I have a great number of receiving devices .... "

---
,
""": ----: )

13 •

.-t
I

~ -- --

. ~

, .~

i

...
...
. .
... . '"

-c-

SECTION I - ADDENDUM

77

,-

I

.

\~

'" ~ ,? ' v

~-
'"

.-

.. t"::!",,,

~

-

78 THE STREAMS OF LENARD AND ROENTGEN

.. ~ .~

= .- " ,gg

u

.......

(-

...

t·

. .: .
( - -,=~-: C iZ"-, I

b1- c..:(

0

(.
'~--_ ~ 1L_ __ '

\......=: ' ~.*

"
<
"

I oJ '

-

SECTION I - ADDENDUM

79

- -1 ..~ .......

~ ~ ~.'

"

.

~~~ .,
- ...J-41-1/'"" 'j

.. ,~ IJ T 0

~, j~

~.

i ' .J

T. ,

,

" I

..;

U

>.....

80 THE STREAMS OF LENARD AND ROENTGEN

~

F
.

-

(

"" S.

~. -=E)~ ...

. ....

~-

b'"

.....
~

..-'.- "

.

l

.

C r - .~ . /

"

I t

..

- J-

It

SECTION I - ADDENDUM

81

·.

"

, ,'4
..... - .

---

- (,

"

...

Sa
"

~

~

~.~ ~
"

-' .. --, ,~--:~ "

~
"

--.

"

...-'

" _m:=:

- ..

E:

.-.-..;$

"

-'

Section II

THE HlJR1FUL ACTIONS OF LENARD AND

the Editor Electrical Review:

The

extending use the Lenard Roentgen

or

bulbs as implements of physician, or

as instruments of research in laboratories, makes it desir-

particularly view

possibility of certain hurtful

actions on human

to investigate the nature of

influences, to ascertain the conditions under which

they are

to occur and --what is most important for

practitioner- to render all injury impossible by the

vance certain

the employment unfailing reme-

dies.

As I have

in a previous communication to your es-

journal (see Electrical Review of December 2,

1896), no experimenter need be

from using freely

the Roentgen rays

of a poisonous or deleterious ac-

tion, and It is entirely wrong to give room to expressions of

a such as tend to impede the

and create a

against an already highly

and more

promising discovery; but it cannot be denied that it is equally

uncommendable to ignore dangers now when we know that,

under certain circumstances, they actually exist. I consider it

the more necessary to be aware these dangers, as I

see coming into general use of novel apparatus, capable

of developing rays of incomparable

power. In scien-

tific laboratories the instruments are usually in the hands of

persons

in their manipulation and capable of approxi-

mately estimating the magnitude

effects, the omis-

sion of

precautions in the present state of our

knowledge, not so much to be apprehended; but the physi-

cians, who are keenly appreciating the

benefits de-

rived from the proper application of the new principle, and

numerous amateurs who are

by the beauty of

the novel manifestations, who are passionately bent upon