zotero-db/storage/48Y68IGE/.zotero-ft-cache

68

MONTHLY WEATHER REVIEW.

FEBRUAR1Y9,16

The wind direction during and immediately following planation is untenable, for no regions have been discov-

the observation of a ha.10 seems to play an im ortant part ered presentsing the phenomenon of 'a continual return

in its verification as a rain pro$ostic. Of tEe 168 halos current, and apart froni this fact, the esistence of a cir-

recorded, 94 were :Lttendecl or ollowed hp etisterly winds culation of the kind depicted would necessitate that the

and falling pressure. Of these, 82, or 87 per cent, were electromotive forces a.round closed paths, in which the

followed by precipitation within 48 hours. This result,is flow was taking place, would have to be of the order of

E Y im ortnnt, in view of the fact that of the total number magnitude of 105 volts. F:Zeetrostnt.ic forces can contri-

of alos recorded, but 99, or 59 per cent, were followed by bute nothing whatever to u line inte a1 around a closed

rain or snow within 48 hours.

circuit. A consideration of such va ues of the line inte-

Un;timcaZ &:.is )Imp, Fort Worth, Tex.--Cninples halos gral as could be obtained on the basis of the change of
. are rare inclee(f. Even the 46'-hdo ocmrs but infre- magnetic induction due to the earth's magnetic field From the time angular measurements were through a closed circuit, or of the motion of the earth

r rstt lmyade at this station, seven 46"-htilos litwe been re- and atmosphere in the magnetic lines of forceof the earth

corded. On the evening of May 23, 1901, two parhelia shows that, apart from the circiinistance that they would

were noted as the sun was about IOo above the western he of n nature unsuitable to correspond to the facts, they

horizon. They a peared on the edge of u bank of alto- would be of an order of magnitude entirely too small to

stratus clouds. 8etwcen this edge and the horizon the play any appreciable art in the phenomena.

' R sky was clear, while above the clouds were so dense as to mie various possib e ty es of hypotheses which may
obscure all evidences of the parhelic circle [ ? 1. The par- be made to account for t e maintenance of the earth's

helia were about 23' distant from the sun.

charge are capable of being grouped under thrse heads:

At about 6 p. ni. on July 2, 1914, a coniples halo with (1) We may imagine that negative electricity is fed into

three parhelia was observed. The two brightest parhelia the earth from the outside in some unspecified manner.

were vertically above and below the sun, while the par- In this case i t will bo necessary to assume that the vertical

helion to the south or left of the sun was but little more conduction current is dissipated again into SpaFe.

than an irregular splotch of light. The phenomenon (2) We may imauine that negative electricity is s u p p h d

lasted about 45 minutes, and O C C U I T ~ during a general c.ontinuous1y to &e earth and positive electric.ity to the

rain over western Tesas; for this reason it is supposed atmosphere a t dl places. (3) We may imagine that

that this station was in the outskirts of the alto-stratus negative electricity is supplied continuously to the earth

cloud region. No color was observed in the phenomenon, and positivo e1ec.tric.ity to the atmos here, the supp

and no rain followed at Fort Worth within several days. taking place, however, over only a !limited region a t

Many of the 22O-halos occur with a cirro-stratus over- any one time.

flow which precedes the inconiing high. These halos are Considering the hypotheses of the first type, it turns out

almost invariably followed by northerly winds and rarely that in view of the fact that the earth is a comparatively

by precipitation. Local thunderstorms are frequently good conductor of electricity, the charge will distribute

preceded by halos, usually 'solar and occurring during the h e l f uniformly over the earth's surface. The known fact

morning hours. These halos are followed by the usual that the conductivity continually increases with altitude

meteorological conditions preceding a thundershower. to a high value is all that is necessary to insure that thin
f It is also observed that halos occurrm with brisk south will arrange themselves so that the positive cha e in t e
P T winds and falling pressure will not be ollowed by rain if atmosphere is equal to the negative c.harge on t e earth.

the wind shows n tendency t o inc,rease in velocity and Considering the hypothesis of type 3, it turns out that

shift to the southwest!,hut that hnlos followed bv soutsh- in regions whero the replenislimont of charge to the earth

P west winds rind risiiio pressure will nlmost invariably be and titmosphere is not taking place, the otential-

followed by ruin w i t h 24 hours.

gradient =id earth-air current-clensjty wou d, under

Halos are not infullihle weather signs, but when prop- ordinary conditions, c~uiclilyf d to a11insignificrtnt d u e .

erly considered in conjunction with other fcntures they If, liowever, a very high vaho is assumed for the conduc-

serve as a material aid to the forecaster.

tivity of the upper atmosphere, this difficulty to some

d extent vanishes, and the assum tion of a rephnishment
of the charge at one place is su cient to account for the

maintenance of atmospheric-electric phenomena at all

OBIGm AND MAINTENANCEOF THE EARTH'S ELECTRIC CEKRGE.'

places. A discussion of several former theories is given; among

By W.F. G . SWANN.

others, those of Elstor and Geitel and of Ebert. In theso

(Read at the special meRting on atmospheric physics of Section I3 9merican Association lor the Advancement 01 Science, San Francisco, Aug. 5, ii115.) [Author's abstract.]

thoories a separation of positive and negative. electricit
d takes place in such a way that.ne ative electricity is 1 t
H on'the earth and positive is supp led to the atmosphere.
The positive charge is carried upward by the ascending

The aper consists of two parts. Part I is devoted to a air currents, and in the steady state; the convection cur-
Y enera discussion of certain broad princi les which n u s t rent so produced must be equal and opposite to the con-
% %e considered in the formation of any t eory of atmos- duction current. Apart from the objections which have

a. heric-electric phenomena, and to a consideration of
Former theories. I n Part I1 a new hypothesis is 110visionally forniulated, and its consequences are trace
Part I commences by considering the possibility of a
9 general circulation in the atmosphere b which the n g n -
tive electricity flowing upward at one p ace is conducted

been raised by others against the Elster and Geitel theorg, it is shown that, owing to t,he conductivity of the atmosphere, the rising positive electricity would become de-
fl voured, as it were, before it had reached any reat alti-
t,udes, and the net result is that on such a t eory the otential-gradient and earth-air current-density would

B down at.sonie other place. It appears that such an es- { e ex octed to diminish to practicdy a zero value at altitu es of the order of maggtude of 1,000meters, whic.h

1 Reprinted from C'arnegle Institution of Washington. Ywbook No 14 lor the venr
1915 pp. 339441. (Tautof the paper appears in full In Terrmtrlsl G e t i s m , " 6ep ternher, 13l5,40:105-126.)

is contrary to the results of balloon experimenh. The objection here cited applies to any form of theory in

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~ ~ A E19Y16.,

MONTHLY WEATHER REVIEW.

69

which the convection current is supposed to balance the In the simplest case, where talierate of emission of cor-

rxnduction current.

pusclos and the nvcmpc? rango of a corpuscle are inde-

The hypothesis provisionnlly foriiiulnt~odin Part, I1 pc?iir1oiitjof tlic a1t.itudc, the! corpuscular current-density

consists in assuming tlint (?:1c11 cuhir c.entinitit)c!rof bhc :uid c.i)iiwquniitlythc c.onrluct,ioncwrrmt-density should

atmosphere emits negative corpuscles of :I poii(!t.r;it.ii)g ( ~ O ~ T H I L Y t~,?o Imwtirdly R mrc, vttlue nt an altitude com-

power sufficientlygreat to eiidde t.lioiii to tmvtd t>l-irough piirddt! with thc average range of a corpuscle. In the

considerable thicknesses of the zitniospliere. The t?art.li iiioro gtxierd ciise whore the rate of corpuscular emission

d l absorb tho corpusc.lt?swhich f d . upem it., t ~ a dit,s and t'licr rango of the corpuscles increaseswith the altitude,

potential will rise, in a negative S ( ~ R C ,until t,lia negat.ire thc ritriat,ion of t.hc co~iiluct~iociui rrent-density with dti-

conduction-current,hack to the various patrts of t,lic?ntmos- t4udehecomes iiiore coniplos, mil it beconies possible in

phere balances the char@ offect due to t.he ospulsion a nst,urnl wny to explain on these linns t8hegeneral fea-

of the cor usclos. The t o t d positivo ctharge in tlie :itmos- tures of tho variations of tlie conduc.tion current with

phere wilfof necessity hc: cqud to the iiegat.ivochargo 011 alt,itude in so frtr ns this variation is known. The argu-

the surface of the earth. In the stcndy s t d o t,hercsultnnt iiiont in this connect.ion is too involved to be made clear

downward corpusdar c,urrent.at, nny dt.it.ucle will just in an nbstract, and a, similar roinark ap lies to a c.onsid-

balance the upward coiiductioii curront at, tliat nltit,uclo. erat>ionof the cluesttionof nniiual and $urnal variation ;

A general considerabion of t,hc ordor of n i q y itwle of the it nuiy be remarked, however, that the more prominent

phenomena conceiiied shows that it is only necessary to foatures of these variwtions fall into natural line with the

8saunie an estremely snitdl rats of eiiiissioii uf corlmscles conclusions resulting from the developnient of the

t per cubic centimeter, and though the degroo of mietm- hy othesis.
tion necessar for these corpuscles is grt?atcr t imi ainv xi conclusion, it is to be remarked that there is con-

we are famil?ar with in laboratory esperiniaits, R fuh siderable latitude in the esact nature of the hypothesis

consideration of all the circunistnnces shows that the which niny be formulated in order to account for the

assumption is not as unreasonnble as might)ab first sight general features of atmosi>heric-electricphenomena dong

be supposed.

the above lines.

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