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IX. Wave-length Determinations and General Results obtained from a Detailed

Examination

o fSpectra Photographed at the Solar Eclipse o f January 2

1898.

B y John E vershed, F .R .A .S.

Communicated

byDr. A. A. R ambaut, F.R.S.

Received December 12, 1900,—Read Jan u ary 17, 1901
[Plates 10-12.]

The results are here given of a detailed study and measurement of a series ot ten spectra, photographed by me with a small prismatic camera, at the eclipse camp of the British Astronomical Association stationed at Talni, India.
The instrum ent referred to had an aperture of 50 millims., and a focal length of about 890 millims. I t wTas fitted with two crown-glass prisms, each of 60° angle, placed in front of an ordinary visual objective, the component lenses of which were slightly separated in order to shorten the focus of the ultra-violet rays relatively to those of the visible spectrum.
[The prisms, which were set at minimum deviation for K, were originally intended for use in a spectroheliograph designed by Professor H ale, and were used by him in an attem pt to photograph the corona in sunlight. They were made by the Zeiss Optical Company, of carefully selected glass, and are 59 millims. in height and 65 millims. measured on the faces, giving an effective aperture of about 42 millims. The total thickness of glass, or mean length of path traversed by the rays in glass, is therefore 65 millims.— March 9, 1901.]
The camera box was fitted with a long sliding plate-holder, moved by rack and pinion across the field of the lens and at right angles to the length of the spectrum. By this means it was possible to change the plates and make the successive exposures at very short intervals of time.*
In all the eclipse negatives obtained with this instrument, the extension of the spectra in the ultra-violet is greater than had been anticipated, and the density of the silver deposit is surprisingly uniform throughout the spectrum. In this connec­ tion it is of interest to compare the eclipse plates with a series of trial plates made

* For a full description of the methods of working see “‘ Report on the Indian Eclipse of 1898,’

published by the British Astronomical Association. (295)

16.11.1901.

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382

MR. J. EVERSHED ON WAVE-LENGTH DETERMINATIONS, ETC.,

in England for the purpose of securing a good focus over the greatest possible range of spectrum. In these preliminary trials the prismatic camera was mounted in front of a large reflecting telescope, the eyepiece of which was replaced by a slit receiving

light from a clear sky. All the spectrum photographs obtained in this way are very dense in the region
near G compared with other parts of the spectrum, and those which are correctly exposed for G give only a very feeble impression of the spectrum in the nltra-violet above K. A very long exposure gave an extension nearly as great as in the eclipse negatives, but the image is extremely feeble at 0 (X 3441), whilst the whole of the lower spectrum from X 3700 down to D is very greatly over-exposed.
In the eclipse negatives, on the other hand, there is only a slight indication of over-exposure at G, and yet the lines are strongly shown up to the limits of the plates, one of which extends to X3340. (Compare fig. 2 with figs. 1 and 3 in Plate 10.) The same kinds of plates were used in both cases, and the very satisfactory results obtained at the eclipse are probably to be attributed to the extreme dryness of the air in Central India at the time of the eclipse.
The following table gives the approximate exposure times, the plates used, and the limits to which the spectra can be traced in the ten eclipse negatives. As I was working without any assistance, the times of exposure could only be very roughly estimated. In the case of the four cusp spectra, the times have been calculated from measures of the width of the strip of continuous spectrum.

Number.

Exposure times.

Plate used.

Spectrum

Limits of

photographed. wave-length.

seconds.

A.

A.

1

Second contact - 20 (inst.)

Edwards’ isochromatic

Cusp

336 to 590

medium

2

„

„ - 10 (inst.)

Ditto

Cusp

340 „ 590

3

,,

,, — 2 to + 2

Ditto, instantaneous

Flash

334 „ 600

4

„

„ + 8 (inst.)

Ditto

Chromosphere 343 „ 580

5

,, + 40 to + 75

Ditto

Corona

335 „ 590

6

,,

,, + 76 to + 85

Ditto, snapshot

f Corona and

350 „ 590

7

+ 86 to + 110

Ditto

\ chromosphere 344 „ 656

8

Third contact + 1 (inst.)

Sandell triple coated

Flash

345 „ 530

9

„

„

+ 9 (inst.)

Ditto

Cusp

345 „ 530

10

»

» +19 (inst.)

Ditto

Cusp

345 „ 530

All the exposures made yielded good negatives, and Nos. 1, 2, 3, 4, and 7 were selected for measurement. The first five spectra of the series are nearly perfect in focus between the limits X390 and X340, but the remaining five, exposed after mid­ eclipse, are not quite so satisfactory, the focus being good only in the extreme ultra­ violet, from 370 to 340.
Owing to the imperfect chromatic correction of the lens used, it was found necessary to incline the plate-holder about 7 degrees from the normal to the axis of the instru­

OF SPECTRA AT THE SOLAR ECLIPSE OF JANUARY 22, 1898.

383

ment in order to obtain a good focus over a long range of spectrum, and the slight shift of the whole spectrum in the direction of its length, which occurred when the chromosphere arcs changed from the east side of the sun to the west, was sufficient to spoil the focus for most of the spectrum, and shift the region of good focus further towards the more refrangible end than had been allowed for.
I t was found possible, however, to make fairly good measures of all the lines shown in No. 7 spectrum.

Photographs of the Cusp before Totality.

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Spectra Nos. 1 and 2 (Plate 10, fig. L).—The first two photographs of the series are mages of the cusp spectrum, the exposures being made 20 and 10 seconds before totality respectively. At the moment when the first exposure was made, the strip of photosphere still uncovered had a width of at the centre of the cusp, and this had diminished to 4" only when No. 2 was exposed. The cusp therefore acted the part of an exceedingly fine slit, and gave beautiful images of the Fraunhofer lines.
The two images obtained may be considered together as they are alike in every respect, excepting in the width of the continuous spectrum. This is 5'20 millims. in No. 1, and 4'78 millims. in No. 2, the moon’s diameter on the plate measuring 8’45 millims. The continuous spectrum shows most of the features of the ordinary Fraun­ hofer spectrum, the dark lines being represented by very sharply defined curved arcs. These are, however, very much less dark than the lines in the spectrum of ordinary sunlight, and the hydrogen lines ft, y, and 8 are not present as dark lines at all. H and K are broad and dark, with an irregular reversal at one point showing motion in the line of sight.
W ith the exception of the absent hydrogen lines the relative intensities of the dark lines in these spectra appear to be identically the same as in the Fraunhofer spectrum throughout the whole region photographed, but the cusp spectra have a pale “ washed-out ” appearance when placed beside photographs of the spectrum of ordinary daylight, and this peculiarity does not seem to be due to any accident of exposure or development.* (Compare the dark lines in figs. 1 and 3, Plate 10, with the corresponding lines in fig. 2.)
* [After returning to England a set of photographs of the Fraunhofer spectrum was obtained with the same prismatic camera, for comparison with the cusp spectra. These were obtained in the same manner as the preliminary trial plates mentioned above, using a reflecting collimator and a slit.
In order to reproduce as closely as possible the form of the solar cusp a circular slit was used, this was formed by a round hole cut in a plate of brass and nearly covered by a circular disc of slightly larger diameter. The hole was made to subtend an angle of 32' at the prisms, and the ratio of the diameters of the hole and disc was made the same as th at of the sun and moon at the eclipse.
In making the exposures the slit was simply directed to a clear sky at a considerable altitude. Fig. 2, Plate 10, is a reproduction of one of the spectra so obtained, in which the breadth of the band is the same as th at of the cusp spectrum in fig. 1. The angular width of the slit was therefore the same as that of the solar cusp at the moment when the cusp spectrum was photographed (about 8" at the middle point).— March 9, 1901.]

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MR. J. EVERSHED ON WAVE-LENGTH DETERMINATIONS, ETC.,

The bright radiations of the chromosphere are in no cases strong enough to show as bright lines upon the continuous spectrum, although they are strongly impressed along the borders, where they form in many cases a continuation of the dark arcs of the Fraunhofer spectrum. The very strong bright arcs, H and K, can be traced round the limb of the moon for a greater distance than any others.
No. 2 spectrum appears to have been under-exposed and the bright arcs are rather difficult to detect upon it, although the exposure was made within 10 seconds of second contact.
Measures were not made of the bright lines in either spectrum as they are not very well adapted for accurate determinations. All of them can be identified with the stronger lines in No. 3 spectrum.

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Methods o f Measurement and Reduction o f the Spectra.
The Fraunhofer spectrum was carefully measured in both cusp spectra and identified line by line with H iggs’s photographic map of the normal solar spectrum.
As these measures form the basis for the determination of wave-lengths in spectra No. 3 (flash) and No. 4, it is desirable to give a brief account of the methods adopted.
I am indebted to Dr. Hambaut for the loan of an excellent millimetre micrometer belonging to the Kadcliffe Observatory.
This instrument consists of a microscope mounted on a sliding frame, and moved by a long screw with a pitch of 1 millim. The head of the screw is divided into 100 parts, and by estimation can be read to '001 millim. All the measures were made upon this micrometer.
Fach spectrum was measured completely three times over, using different sections of the screw and different readings of the head each time. By this means any systematic differences due to errors in the screw were eliminated in the mean result, and accidental mistakes in reading the divisions were readily found and corrected. No evidence of any systematic error in the screw was, however, detected, and the three sets of measures of spectra Nos. 1 and 2 showed a very satisfactory accordance throughout the whole length measured.
In measuring a line, the mean of three settings of the spider lines was taken as the scale reading of the line, and in the final mean result, in which the two cusp spectra are combined, every line represents eighteen settings of the spider lines.
The measures of the two cusp spectra when compared were found to agree as closely as two separate measures of either spectrum, thus proving th at no change had occurred in the dispersion from any cause. The two spectra were therefore considered to be identical, and the measures were combined.
From the final mean of the six sets of measures about thirty well-defined and isolated lines were selected as standards ; these are all distributed through the ultra­ violet portion of the spectrum more refrangible than H. In the region between

OF SPECTRA AT THE SOLAR ECLIPSE OF JANUARY 22, 1898.

385

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H and F about twenty-six lines were used, which are, however, not so well defined or

so satisfactory as standards as the others.

In constructing a scale of wave-lengths for the reduction of the bright-line spectra

(Nos. 3 and 4), the best defined known lines between D and H in these spectra were

also selected as standards, and used together with the twenty-six cusp spectrum lines.

But in the ultra-violet the scale depends entirely upon the standards of the cusp

spectrum, the whole of the lines in this region in Nos. 3 and 4 (including the

hydrogen lines) being treated as unknown. A careful comparison made between

measures of known lines in Nos. 3 and 4 spectra and the mean measures of the two

cusp spectra shows th at it is safe to assume th at all the spectra obtained before mid­

eclipse may be considered to be identical as regards dispersion.

A sufficient number of standards well distributed throughout the entire spectrum

being thus obtained, the approximate relation between scale reading and wave-length

at all points in the spectrum was next determined by graphical methods, and from the

interpolation curve obtained it was easy to compute the scale reading corresponding

to a number of definite points in the spectrum separated by equal intervals of wave­

length.

The scale reading corresponding to each 50 tenth-metres of wave-length was in this

way computed, taking in each case the mean result given by three or four standard

lines situated near ; and the values thus obtained were finally slightly corrected

by smoothing differences until fifth differences were made to increase in a regular

progression.

The smoothed values in no case differ from the values derived from the measures by

quantities greater than the uncertainties of the measures themselves. The mean

difference in the best defined portion of the spectrum X4100 toX3400 is'0016 millim.,

and the greatest difference '005 millim., the latter corresponding to '15 tenth-metre

at X4100 and '07 tenth-m etre at X3400.

In the visible spectrum the definition under the microscope is very poor in all the

negatives except No. 4, and the measures in consequence are not very consistent, but

for the sake of completeness every line has been measured, and an accurate scale of

wave-lengths constructed for the entire range of spectrum photographed.

From the accordance between the different sets of measures of the bright lines in

No. 3 spectrum the probable errors of the wave-length determinations given in

Table I. (p, 404

etseq.) would appear to be about '15 tenth-metre at X 4000, decreasing

to '05 tenth-m etre at X 3400.

The Bright-lineSpectra.

Spectrum No. 3 (Plate 11, fig. 1).—This negative was exposed at the moment when

the dark lines of the Fraunhofer spectrum were seen to disappeai and innumeiable

bright lines flashed out across the strip of continuous spectrum winch still lemained

visible.
VOL. C X C V II.----A.

3 D

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38G

MR. J. EVERSHED ON WAVE-LENGTH DETERMINATIONS, ETC.

I was observing with a slitless spectroscope attached to a 3-inch equatorial, and made the exposure as nearly as I could judge 2 seconds before the last trace of continuous spectrum vanished. The plate was given an exposure of at least 4 seconds in order to impress the fainter details.
In the photograph the strip of continuous spectrum is divided into four parts by longitudinal dark bands due to irregularities in the moon’s limb. Most of the bright lines of the chromosphere and flash spectra are visible as bright lines upon the continuous spectrum, but the helium lines a t A 4026'5 and A. 4713'2 are an exception, and they cannot be traced even in the dark spaces between the strips of continuous spectrum, although strongly impressed on either side. The helium line at A 4472 is visible, but weaker in the intermediate dark spaces. No trace of any absorption lines can be detected in any part of the continuous spectrum.
The total depth of the chromosphere as indicated by the calcium lines H and K is 11//*6, these lines extending over an arc of 124 degrees. The hydrogen lines , y, 8, ?, and the titanium lines at A 3761‘5, A 3759'3, and A 3685’3, as well as the helium line D/;/, extend over an arc of about 102 degrees, implying a depth of
The bright arcs of the flash spectrum proper are approximately of the same length. On the north side of the continuous spectrum they are cut off abruptly by a dark band, due to a projecting lunar mountain, and two similar bands interrupt the lines on the south side.
Most of the fainter flash lines can be traced over an arc of 40 degrees of the sun’s limb, indicating a depth of 1"*3, or nearly 600 miles.
A great many of the stronger lines, however (chiefly titanium, iron, and magnesium lines), extend faintly far beyond this limit, and can be traced over an arc of nearly 70 degrees, the depth implied in this case exceeding 4", or 1800 miles.#
A few very faint lines due to the very lowest layers of the chromosphere are also indicated in the best defined portion of the negative. These are visible only upon the strips of continuous spectrum, and.do not extend beyond.
Probably only a small proportion of the finer lines which were actually present at second contact are shown in this photograph. In the green region near this is certainly the case. The most striking feature seen when observing the spectrum under high dispersion and without any slit was the immense number of excessively fine bright arcs which appeared in a short section of the spectrum (including the b lines) at the moment when the exposure was made. Yet very few of these lines appear on the photograph, partly perhaps on account of the poor focus in this region.

* [Iti estimating depths from the lengths of the arcs the moon’s apparent semi-diameter is taken at 997"-0 and th at of the sun 974",9. A uniform distribution of the gases round the limb is of course assumed, and the results from No. 3 spectrum indicate the depth measured from the photosphere to the upper limit to which each particular radiation can be traced. The depth of photosphere left uncovered by the moon in this photograph being quite inappreciable, the limb of the moon may be considered as being coincident with that of the sun at the point of second contact.— March 9, 1901.]

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OF SPECTRA AT THE SOLAR ECLIPSE OF JANUARY 22, 1898.

387

The continuous spectrum of the corona is strongly marked on this photograph, but only one tru e corona line is visible, the green line a t X 5303. This line can be traced only on the eastern poition ol the moons limb, and, unlike the chromosphere arcs it is very variable in intensity, being strongly marked about the positioij angles 60° to 70°, and 100°, where the continuous spectrum is also strong, but extremely weak or entirely absent in other parts of the limb.
The results of measures of the corona line on this plate and No. 7 spectra are given on p. 401.
[In the reproductions of the bright-line spectra shown in Plate 11, the position angles may be inferred from the fact th at the direction of dispersion is also the direction of the moon’s path across the sun, the point of second contact (P.A. 56°) being at the centre of the arcs on the right-hand side, and third contact (P.A. 236°) at the centre on the left. The angles are reckoned from the north point through east, south, and west.
The upper edge of each spectrum, therefore, represents the south-east limb, and the lower edge the north-west limb. The diagram below, showing the prominences in their correct positions, will make this clear. The broken lines indicate the positions where the green corona line is strongest on the negatives. In the reproductions it can be faintly traced on the east limb, where it persists throughout totality, thus proving it to be a true coronal radiation, since the chromosphere on this limb was entirely hidden by the moon after mid-eclipse.

S =160°

b VISecond aonC&cC,

In fig. 5 the interrupted coronal arc is perhaps best seen ; it almost meets the oppositely curved chromosphere arc D"'.
The wave-length scale at the top of Plate 11 must be understood as applying only to fig. 1, for which it was constructed. The designation of the principal lines in the spectra are given underneath fig. 5, at the bottom of the plate.
3 i) 2

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388

MR. J. EVERSHED ON WAVE-LENGTH DETERMINATIONS, ETC.,

For further facilitating references to the bright lines a plate is given of the ultra­ violet region of the spectrum of the lower chromosphere. In this a wave-length scale is given above and the designation of some of the principal lines below. The plate has been prepared by purely automatic methods from the original negative taken at second contact. By photographing a longitudinal section of this negative with a cylindrical lens interposed, the short sections of the chromosphere arcs are spread out into straight lines.
Great care was taken to exclude spurious lines due to defects in the film or to dust on the slit. By using a rather wide slit these imperfections have been reduced to a minimum, although this involved a slight sacrifice of definition and loss of detail.— March 9, 1901.]
Spectrum No. 4 (Plate 11, fig. 2).—The exposure in this photograph was probably less than half a second duration, and was made several seconds after closing No. 3 exposure.
The continuous spectrum of the corona is faintly impressed* and the green line is ju st traceable at the points where it is strongest in No. 3 spectrum. The chromo­ sphere arcs H and K and the hydrogen series are narrow and well defined, the latter both in the visible spectrum and the ultra-violet. The three titanium lines at \\3 7 6 P 5 , 3759'3, and 3685'3 are shown as exceedingly fine threads, extending over an arc of about 60 degrees; they are distinctly stronger than the line Hr; but fainter than H£. The hydrogen lines /3, y, 8 and the calcium lines H and K can be traced over nearly the same extent of the limb as in No. 3 spectrum.
The prominences are well defined in this negative and their spectra exhibit some interesting features. There are seven prominences clearly shown, which I have designated by the letters of the alphabet in the order of their position angles, as follows :—

Prominence. A .. B .. C .. D .. E .. F .. G ..

Position angle.

. . .

28°

.. .

59

. . .

99

. . . 126

...

306

. . . 315

...

322

Solar latitude. + 54° + 23 — 17 — 44 + 44 + 53 + 60

All these prominences are about equally intense in the calcium lines H and K ; D is the largest and B and C are the smallest images.
* In preparing a plate suitable for reproduction it was found necessary to intensify the image with uranium. This has made the continuous spectrum of the corona appear very much stronger than it is in the original negative.

OF SPECTRA AT THE SOLAR ECLIPSE OF JANUARY 22, 1898.

389

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In the hydrogen images A, and the group E, F, G are much fainter than the others, and in the ultra-violet the images of these four are very difficult to trace beyond the line Hd. A is however very faintly indicated in the three titanium lines above mentioned.
The prominence C is much brighter in hydrogen than the foregoing and can be traced to the line H/r. The three titanium lines are also clearly shown.
The prominences B and D are the strongest of all in hydrogen, and although very different in size and general character (as observed in H a about an hour before totality) they give practically the same spectra.
The prominence B being situated very near the point of second contact (P.A. 56°) its spectrum falls almost exactly along the centre of the photograph. I t is, therefore, in the best position for accurate measures ; and as the images in the ultra-violet are well defined circular black spots, much smaller and more definite than the corre­ sponding images of the large prominence D, the wave-lengths given in Table II. are deduced from measures of this prominence only. (See p. 411 et seq.)
N early all the lines measured can however be traced also in I ) ; there are fifty-two altogether and all of these are accounted for by the elements H, He, Mg, Al, Ca, Sc, Ti, Fe, and Sr.
A remarkable feature in the spectra of the prominences B and D is well shown in this negative. The prominence D shows traces of a continuous spectrum in the region less refrangible than H, which is absent in B. Both prominences, however, give a strong continuous spectrum in the extreme ultra-violet, beginning abruptly at X3668 near the end of the hydrogen series, and extending as far towards the smaller wave-lengths as the impression of the corona spectrum can be traced.
The actual limit to which the extremely narrow streak due to the smaller promi­ nence B can be traced is at X3435 ffi.
This feature is shown more or less distinctly on all the negatives taken during totality. In No. 3 spectrum as well as No. 7 a considerable arc of the chromosphere itself shows the ultra-violet continuous spectrum, all the flash spectrum lines more refrangible than X3668 being immersed in a uniformly shaded band which is absent in the less refrangible region.
(In the reproductions this delicate feature is lost in all the images except fig. 2. I t is shown more satisfactorily in the enlarged image in Plate 12.)
Spectrum No. 5 (Plate 11, fig. 3).—This was exposed during about 40 seconds near the time of mid-eclipse. The exposure began about 10 seconds after the dis­ appearance of the chromosphere on the east limb and ended immediately after its partial reappearance on the west limb.
The continuous spectrum of the corona is strongly impressed, and can be traced as far as X3300 in the ultra-violet. The green corona line is well shown on the east limb; it is distinguished from radiations due to the chromosphere by its diffuse character and distinct maxima of intensity corresponding with the brighter regions of the

390

MR. J. EVERSHED ON WAVE-LENGTH DETERMINATIONS, ETC.

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inner corona ; it is most intense at position angles 60° to 78° and 95° to 105°. On the west side it can be traced at about position angle 250°, but is extremely faint here.
No trace of any true corona line can be made out in the blue or violet part of the spectrum, but there is a fairly distinct impression of a line near the end of the plate at X3388, where faint maxima of intensity are indicated on the east limb at the same position angles as the maxima of the green line.
The chromosphere in this negative is represented by the lines H and K only, which form arcs extending over the western limb (P.A. 182°-289°). The prominence C gives the principal hydrogen, helium, and titanium, lines in addition to H and K.
Spectrum No. 6 (Plate 11, fig. 4).—The exposure in this case was of 10 seconds’ duration, beginning about 2 seconds after closing No. 5.
The chromosphere arcs have reappeared in the hydrogen and helium lines on th e west limb, and the former can be traced to H tt. The three strongest titanium lines are also visible, extending over an arc of 60°. The prominence C shows the streak of continuous spectrum starting at X3668 and extending as a fine thread far into the ultra-violet.
The green corona line is faintly impressed both on the east and west limbs, but no other corona line can be made out with any certainty. There is, however, a doubtful impression of a line extending pretty uniformly over the west limb at a point in the spectrum a little less refrangible than H (X 398/399). I t cannot be traced at all on the east limb, at the points where the green line is most intense, and if it is a real corona line, the substance producing it is evidently not the same as th at which gives the green line.
Spectrum No. 7 (Plate 11, fig. 5).—The exposure of 20 seconds’ duration was started immediately after the last and ended only 3 or 4 seconds before the photo­ sphere appeared.
In the chromosphere spectrum H a is well shown, and in the ultra-violet the hydrogen lines can be clearly traced to Hco. Many of the stronger flash-spectrum lines are visible along the central portion of the photograph extending over arcs of from 40° to 60°. The wave-lengths deduced from measures of these lines are given in Table I., and in the region between X340 and X360, where the focus is good, the results are as accurate as those obtained from No. 3 spectrum.
A conspicuous feature in this photograph is the shaded band of continuous spectrum in which the more refrangible lines of the flash spectrum are immersed. It is absent in the region less refrangible than X 3668, and corresponds to the fine streak or tail which the prominence C shows in all the photographs obtained during totality.
The green corona line is better defined in this photograph than in any of the others. The positions of maximum intensity correspond precisely with the bands of continuous spectrum due to the brightest regions of the inner corona. The position angles measured on this plate are as follows :—

OF SPECTRA AT THE SOLAR ECLIPSE OF JANUARY 22, 1898.

891

East limb . W est limb

Position angle of maximum intensity.
r 5 7 °to 78° 1 94 „ 100
235 „ 254

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As in No. 6 spectrum there is an exceedingly faint impression of a corona line

near H and extending over the west limb, but excepting this no trace of any other

lines are visible. The image, unfortunately, is too feeble in the extreme ultra-violet

to show the line at

X3388 found on No. 5 spectrum.

Spectrum No. 8.—This negative was exposed for about half a second almost at the

moment of third contact. The reappearing photosphere has been impressed as four

very narrow streaks of continuous spectrum. The flash spectrum is well developed,

and the whole length of the spectrum is crowded with bright lines extending

between and across the strips of continuous spectrum. The majority of the lines due

to the lower chromosphere extend over an arc of 55°, the depth implied in this case

being 2//,5.

The focus in this negative is unfortunately very poor throughout the spectrum,

and no measurements were made for determining wave-lengths. The spectrum was,

however, carefully compared with No. 3 by means of enlargements of each spectrum,

which were made to correspond approximately in scale. Superposing one spectrum

upon the other it was found th at the two appeared to be identical in all respects. If

any differences exist at all between the spectra of the east and west limbs of the sun

they can only be found in the finer details, which in No. 8 are lost by reason of the

imperfect focus.#

The Cusp Spectra after Totality.

Spectra Nos. 9

and 10 (Plate 10, fig. 3).—These were given an exposure of les

than half a second at about 10 and 18 seconds after third contact respectively. They

are both very similar to the first two spectra of the series, but apparently the

exposures were appreciably of longer duration than those made before totality, and

the bright lines bordering the continuous spectrum of the photosphere are in conse­

quence much more strongly marked than in Nos. 1 and 2.

As in all the spectra of the west limb the focus is imperfect except in the ultra­

violet region more refrangible than X 360. The bright lines are, however, fairly well

defined along the south edge of the cusp.

The Fraunhofer spectrum is not nearly so well developed in these spectra as it is in

Nos. 1 and 2. This may be due to over-exposure as well as poor focus, but at the

ultra-violet end where the spectrum is less dense and the focus good, the dark lines,

* No figure is given of this photograph as it was found impossible to produce a satisfactory plate suitable for reproduction.

392

MR. J. EVERSHED ON WAVE-LENGTH DETERMINATIONS, ETC.,

although clearly visible, are not nearly so strongly marked as in the corresponding negatives of the east limb before totality.
All the more conspicuous lines which are characteristic of the flash spectrum can be distinguished along the south edge of the cusp in both No. 9 and No. 10 spectra.

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General R esults and Conclusions.
TheFlash Spectrum.
In comparing the wave-length values of No. 3 and No. 7 spectra given in Table I. with R owland’s wave-lengths of the absorption lines in the solar spectrum, it is at once apparent th at practically every strong line in the latter is present in the lower chromosphere as a bright line. In the region between 3340 and 4410 there are 58 strong dark lines with an intensity exceeding 8 on R owland’s scale of intensities. In the flash spectrum (No. 3 photograph) 44 of these lines are certainly present as bright lines ; 6 are probably present, 6 are too near to strong hydrogen lines to be separately distinguishable, and 1 is obscured by H. One line only of the 58 is unaccountably absent, th at at 3788'046 (Fe, intensity 9).
I t is further to be observed th at of the bright lines of the lower chromosphere (hydrogen and helium lines being excluded) the great majority appear to be coinci­ dent with dark lines having an intensity on R owland’s scale not less than 3, and two lines only X 3584'37 and 3812'79 occur in a blank space in the solar spectrum where the lines are weaker than intensity 0.
It may be said generally therefore, with regard to the ultra-violet region, th at the bright lines of the flash spectrum are reversals of Fraunhofer lines, including all the very strong lines (intensity 10 and upwards).
W hilst the positions of almost all the bright lines appear to coincide with dark lines in the solar spectrum, the relative intensities of the lines in the latter are widely departed from in the flash spectrum. A negative of No. 3 spectrum is there­ fore very unlike a positive of the solar spectrum.
When, however, the flash spectrum is analysed into its separate constituents it is found th at the relative intensities of the lines of any one element correspond very closely with the intensities of the dark lines of th at element. In the iron and titanium spectra, which claim more lines of the flash spectrum than any other elements, this correspondence is most clearly shown. There are, as might be expected, many cases where the intensities are abnormal, but by taking the average intensity on R owland’s scale of all the dark lines corresponding to each unit of intensity in the flash spectrum the effects of these are eliminated. These abnormal intensities are probably due to the superposition of closely adjacent lines.
The following tables prove the general close correspondence of intensities in the flash and solar spectrum for iron and titanium. The first column gives the number of flash lines having the estimated intensity given in column 2, whilst the average

OF SPECTRA AT THE SOLAR ECLIPSE OF JANUARY 22, 1898.

393

intensity of the corresponding dark lines is given in column 3. Although the intensities of the bright lines, estimated on a scale of 1 to 10, are not comparable with those of R owland ranging from 1 to 1000, the relation between the bright and dark line spectia is, nevertheless, clearly indicated by the regular progression of the figuies in the last column of both tables corresponding with the progression between 0 and 5 in the middle column :—

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Intensities of Iron and Titanium Lines in the Chrom osphere and in the Solar Spectrum.

Number of lines in flash spectrum.
17 33 25 10

Iron
Photographic intensity.
0 I 2 3

Average intensity of the corre­ sponding dark lines in © (Rowland).
55 7-5 11 3 25*3

Total 85 W eighted mean 1*3 W eighted mean 10 *2

Number of lines in flash spectrum.
5 9 13 9 4 1

Titanium Lines.

Photographic intensity.
0 1 2
0
4 5

Average intensity of the corre­ sponding dark lines in © (Rowland).
U6
3*4 4*2 5*4
7 .7
10*0

Total 41 W eighted mean 2'0 W eighted mean 4*5

The mean intensities given a t the bottom of each column show the greater

intensity of the Ti lines in the chromosphere compared with Fe, and the much

greater average intensity of the Fe dark lines in the solar spectrum compared with

the Ti lines.

The striking dissimilarity in the relative intensities of the lines of different

elements in the bright-line and dark-line spectra is probably due to the

heights to which the gases of the various elements ascend in the chromosphere.

The intensities as they appear in photographs of the flash spectrum are evidently

largely determined by the relative depths of the various gaseous strata, the more

extensively diffused gases giving the strongest bright arcs simply by reason of the

greater radiating area. The low-lying gases, on the other hand, although they may he

VOL. CXCVII.— A.

3 E

394

MR. J. EYERSHED ON WAVE-LENGTH DETERMINATIONS, ETC.

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intrinsically more luminous and denser, give fainter arcs because of the excessively

small angular width of the radiating area.

I t is to he borne in mind th at the flash-spectrum arcs or “ lines” obtained with a

prismatic camera are not true images of the strata producing them, but diffraction

images more or less enlarged by photographic irradiation. The deepest layers

subtend an angle of only

2",representing on the sun about

chromatic radiations from such strata will produce lines which are as narrow as

instruments of ordinary resolving power are capable of defining. The diffraction

image of a shallower stratum will not be narrower in proportion but simply less

bright. A layer of gas 9 miles in depth would, if sufficiently dense, be capable of

producing strong absorption lines in the solar spectrum, yet it would have to be

100 times more luminous than a stratum extending for 2" above the photosphere

to give ecpially strong bright lines in the photograph, even were the moon to remain

stationary at the contact and allow of equal exposures.

But it is obvious that, for the shallow layers, the time during which the plate is

exposed to any radiation is proportional to the depth of the luminous layer, the

advancing limb of the moon cutting off the shallow strata during the exposure;

consequently, for an exposure timed from the moment of second contact and lasting

until the whole depth of

2"had been occulted, the plate wou

9-mile stratum for only oth °f* the- whole exposure. This layer would therefore

need to be 10,000 times more luminous to give lines of equal intensity to those of the

deepest layers.

[In the absorption spectrum the relative intensities between the different elements

must depend on the total number of absorbing molecules of each element encountered

by a ray of light in its passage outward from the photosphere, and not on the

relative state of diffusion or depth of the different gases.

To illustrate these points, which appear to me to be of great importance in

elucidating the relationship between the emission and absorption spectra, we may

consider the typical cases of iron and of titanium in the chromosphere.

The total number of iron molecules encountered by a ray of photospheric light

probably vastly exceeds the number of titanium molecules, since the absorption lines

of the former are among the strongest and broadest in the spectrum, whilst those of

the latter are narrow and mostly weak lines. But the iron vapour is concen­

trated in a stratum close down upon the photosphere, whilst titanium is diffused

through the entire depth of the chromosphere. Hence the apparent intensities of

the emission lines of iron fall considerably below those of titanium.

If the relative distribution of these two elements were reversed without changing

the total quantity of each, the absorption lines would probably not be materially

altered in intensity, but the bright lines of iron would then rival those of calcium in

H and K, whilst the titanium lines would be difficult to detect in the flash spectrum.—

March 10, 1901.]

OF SPECTRA AT THE SOLAR ECLIPSE OF JANUARY 22, 1898.

395

I t thus appears th a t the intensities found in these spectra by no means represent the actual intrinsic intensities of the bright lines of the different elements. Could we obtain a sample of the incandescent gas from near the base of the flash-spectrum layer and examine it close at hand with a slit spectroscope, it is certain th at the relative intensities would differ widely from those in the flash spectrum as observed at an eclipse, and it is possible th a t they would be found to correspond much more closely with the relative intensities in the Fraunhofer spectrum.
From the foregoing considerations it is clear th at the emission lines from the lowest levels of the flash layer must be very difficult to observe, however bright they may be intrinsically. The wide divergence between the flash and Fraunhofer spectra, with respect to intensities, would appear, therefore, to afford no ground for abandoning the original interpretation of the flash proposed by Professor Young from his observation in 1870, and the evidence of these photographs certainly indicates th at the flash does, in fact, represent the upper, more diffused portion of a true reversing stratum.
In the flash-spectrum photograph (No. 3) fifteen elements can be identified with certainty in the lower chromosphere, in addition to hydrogen and helium, and there are three elements doubtfully represented.
Arranged according to their relative intensities, the following four groups occur :—

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Group I.

(Lines strong in flash and in solar spectrum.)

Na . . . atomic weight 23'0

Mg . . . „

„ 24-3

A1 . . . „

„ 27d

Ca . . . „

„ 40-0

Group II.

(Lines strong in flash but comparatively weak in solar spectrum.)

Sc .

atomic weight 44T

Ti . . . 33

„ 48-1

Y . • • ??

„ 51-2

Cr . • • ?5

„ 52-1

Mn . • * ??

„ 55-0

Sr . ‘ • >>

„ 87-6

Y . • * ?)

„ 887

Group 111.

(Lines relatively weak in flash, very strong in solar spectrum.)

Fe

atomic weight 56-0

Ni

587

3E2

396

MR. J. EVERSHED ON WAVE-LENGTH DETERMINATIONS, ETC.,

Group IV.

(Lines weak in flash and in solar spectrum.)

Zr

atomic weight 90'6

C* . . . _ „

„ 12-0

The elements of which the identifications are somewhat doubtful are—

Si Co .
La .

atomic weight 28'4 One line only X 3905*660

,,

,, 59*0 Many Co lines seem unaccountably absent

in the flash

,,

,, 138*5 Two lines only X 4123*384 and X 3649*654

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I t is probable th at the elements of Group I. are diffused throughout the entire depth of the flash-spectrum layer, but become denser near the photosphere. Those of Group II. are possibly absent from the very lowest strata, but are widely diffused in the higher regions; whilst the elements Fe and Ni (Group III.) would appear to he mostly concentrated in the lowest strata where the density is great enough to produce the winged absorption lines.
Group IV. probably represents low-lying elements of small density. The bright lines of the flash spectrum corresponding to Group II. may be considered to he true reversals of the dark solar lines of these elem ents; th at is to say, the whole of the m atter concerned in the absorption contributes to the emission spectra, and the bright and dark lines are practically of equal width. But in the emission lines of Groups I. and III. the radiation from the very lowest region, where the density of each element is considerable, contributes very little indeed to the total light, most of which comes from the higher more extensive regions of low density ; consequently the lines appear narrow and without appreciable shading. These lines, therefore, can only be considered as partial reversals of the corresponding absorption lines. The metallic elements found in the lower chromosphere (including those doubtfully identified) include all the known metals having atomic weights between 20 and 60, with the single exception of potassium. Arranged according to their atomic weights, they are :—•

\r Na Mg La i ^ Ca
Sc Ti V

approximate atomic weight 23

24

55

55

55

5 5

5 5

5 ?

27

40

5*

55

5 5

44

55

55

55

55

55

55

48

51

55

55

55

* Probably the compound cyanogen.

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OF SPECTRA AT THE SOLAR ECLIPSE OF JANUARY 22, 1898.

397

<1 Cr . Mn . Fe . Ni .
.Co?.

approximate atomic weight 52

”

99

99

55

99

99

99

56

9*

99

99

59

99

99

99

59

99

99

99

88

99

T9

59

89

99

99

99

91

Taking the whole series of* known elements having atomic weights from 1 to 100, all the metals are here represented excepting the following:—

Li

approximate atomic weight 7

Be

9

K

39

Cu

64

Zn

65

Ga

70

Ge

72

Bb

85

Nb

94

Mo

96

Of th e nineteen known metalloids, the only ones indicated in these spectra are—

H

approximate atomic weight = 1

He . . .

,,

„ „

4

Cl ... .

„

„

„

12

NJ . . .

„

Si ? . . .

„

„ „

14

„ „

28

None of the elements with atomic weights exceeding 91 appear to be represented in the flash spectrum, unless we include lanthanum (at. wgt. 138). It is probable, however, th at with instruments of much greater aperture and focal length than the one employed in this research photographs would be obtained which would bring to light many of the heavier metals which doubtless exist in the lowest strata of the flash-spectrum layer.
Although it would seem from the above statement that there is a general, inverse, relation between the atomic weight of an element and the extent of diffusion of its vapour above the photosphere, it is evident th at among the elements actually found in the chromosphere this relation does not always hold; thus calcium and titanium ascend to far greater elevations than the three elements of smaller -atomic weight, sodium, magnesium and aluminium.
Unknown Lines.—Only a small proportion of the lines in Table I. remain to be

398

ME. J. EVERSHEL) ON WAVE-LENGTH DETERMINATIONS, ETC.

identified. In the region between

XX3340 and 4000 the

of 225, and all of them are weak lines. The strongest (intensity 2) correspond in

position with dark lines in B owland’s table which have not been identified with

element, and these are given in the following l i s t :—

W ave4ength in flash.
356777 3589-72
3645-35

Intensity.
2 2
2

3655-78

1

W ave4ength in © .
3567-835 3589-773 [3645-429 13645-475 3655*801

Intensity.
4 5 3 3
o

These are the only unknown lines in the flash spectrum with an intensity greater than 1, and it is ju st possible th a t they belong to the same element.

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TheHydrogen Spectrum.

The wave-lengths of the hydrogen lines taken from Tables I. and II. are entered separately in Table III., together with the values computed from Balmek’s formula. The latter were computed for a vacuum and corrected for air in accordance with a table of B unge (‘ Astronomy and Astro-physics,’ vol. 12, No. 5).

In the formula

. ____

~~ Sa( 2 - 4) ’

S is the series number of the line, and a is a constant derived from B owland’s measures of the lines Ha, H/3, and H y in the solar spectrum reduced to a vacuum, the mean value adopted being a = 27418-75.
In obtaining the mean values given in column 4, equal weights are given to No. 3 and No. 4 spectra, both of which are in good focus beyond K, and give equally consistent measures in this region. No. 4 spectrum is, however, much the better of the two in the visible region, where the images are comparatively small, well-defined spots. This spectrum, as already mentioned, consists of a series of images of a very small bright prominence, and very consistent measures were obtained throughout. The good agreement of the wave-lengths of the metallic lines with B owland’s values will be seen on referring to Table II.
The very close agreement of the hydrogen lines with the computed values is shown in column 6 of Table III. (observation — calculation). It will be noticed, however, that the wave-lengths of the more refrangible members of the series are appreciably smaller than the theoretical values, the differences increasing towards the limit of the series. This may be due to the greater uncertainty of measurement of the fainter lines, which are apt to be confused with other lines closely contiguous, or it may possibly be due to a slight progressive error in the scale value for this region.
The results obtained for No. 7 spectrum given in column 7 appear to confirm the

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OF SPECTRA AT THE SOLAR ECLIPSE OF JANUARY 22, 1898.

399

values of the more refrangible lines in No. 3, although they were obtained by

quite independent methods of reduction. The measures of this plate, however,

cannot be given the same weight as those of the other two, the definition being poor owing to imperfect focus.

The lines in the visible spectrum H a, /3, and are entered for the sake of com­

pleteness, but they are not to be compared in accuracy with the ultra-violet lines.

This is largely due to the difficulty in measuring the broad over-exposed lines /3, y,

and

8on No. 3 spectrum, and partly to the small dispersion in this region.

The line 8 appears in all the measures to he largely displaced towards the red, but

this is probably accidental. I t is remarkable, however, th at in R owland’s table of

the solar lines HS is given at \ 4102’000, which is also less refrangible than the

theoretical position, the difference being TO tenth-metre. The almost perfect agree­

ment of the other absorption lines in his table, and the very close agreement of the

best defined ultra-violet lines in Nos. 3 and 4 spectra with the positions assigned by the

formula, suggests th at the wave-length of this line has been erroneously estimated.

Mr. J ewell, however, who made the measures of R owland’s plates, while adm itting

some uncertainty in estimating the centre of the line in the solar spectrum, finds

on re-examining his measures, no justification for altering his original estimate

(‘ Astro-Physical Journal,’ vol. 9, p. 211). I t is very desirable th at accurate measures be made of IIS in the upper chromo­

sphere where the line is narrow and free from interfering lines. The limit of the hydrogen series defined by the formula when s = co is at X3646.

But in the chromosphere spectra the lines fade away to invisibility long before

reaching this point. I would call particular attention, however, to the very

remarkable band of continuous spectrum shown by the prominences and lower

chromosphere, beginning near the end of the tabulated series and extending indefi­

nitely towards the more refrangible end of the spectrum. The interspaces between

the hydrogen lines are quite clear of this continuous spectrum, which begins abruptly

at about 3668. (See Plate 12.) It seems probable th at this faint spectrum may be itself due to hydrogen. In
the absorption spectrum of white stars of Type I., Sir W illiam H uggins has observed an analogous feature. This consists in the rather sudden fall of intensity of the continuous spectrum at about the place of the end of the series of dark hydrogen lines. The enfeebled spectrum continues to run on without further enfeeblement

until it is stopped by the absorption of our atmosphere. This seems clearly to be the absorption effect of the m atter giving the faint con­
tinuous spectrum in my plates, and the fact th at the feature is chaiacteiistic of white stars in which the hydrogen absorption is very strong points to its being due to

hydrogen itself.*

* ‘ An Atlas of Representative Stellar S pectra’ (Sir W illiam and Lady H uggins), p. 85.

400

MR. J. EYERSHED ON WAVE-LENGTH DETERMINATIONS, ETC.

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Helium and Hydrogen in the Lower Chromosphere.

The part played by helium and hydrogen in the lower chromosphere may next he

considered. Helium is probably absent from the very lowest strata, if indeed it is

present at all in the flash-spectrum layer. The lines at XX3634*4, 4026'3, 4471 '6,

and 4713*2 are very weak, or quite invisible upon the continuous spectrum at the

centre of the photograph (No. 3) although strong on either side, whilst the majority

of the lines of the flash spectrum proper are strongly impressed right across the con­

tinuous spectrum. This would point to the absence of helium from the region within

2" of the photosphere.

[But the lines at XX4922T and 5015‘7 appear on the other hand to be strong on

the continuous spectrum and weak at the sides. I t is to be remarked, however, th at

these lines belong to two series of lines in the spectrum of cleveite gas which have

been ascribed to

parheliumyb B unge and P aschen.* I t would seem, therefo

th at these “ parhelium ” lines, whatever their origin, are produced under conditions

existing only in the lower levels.— March 10, 1901.]

The absence of appreciable absorption due to helium in the solar spectrum seems also

to favour the view that this element exists only in a rarefied condition in the upper

chromosphere. This peculiarity in the spectrum certainly does not necessarily imply

equality of temperature between the radiating gas and the photospheric background ;

for the hydrogen spectrum affords a demonstration th a t chromospheric gases at a

lower temperature than the photosphere, can emit strong bright lines without corre­

sponding absorption lines. Thus, in the visible spectrum the dark lines corresponding

to Ha, /3, y, and 8 are sufficient evidence th at hydrogen in the chromosphere is cooler

than the photosphere. But in the ultra-violet the absorption becomes inappreciable

at H£, and beyond this point there are no dark hydrogen lines corresponding with

the strong bright lines in this region.

In the emission spectrum of the chromosphere there is a progressive diminution of

intensity of the hydrogen lines towards the smaller wave-lengths. Nevertheless, the

lines H 77, 6, t, k are still among the strongest lines in the spectrum beyond K. In the

ultra-violet, therefore, hydrogen behaves exactly like helium in the visible spectrum.

The disappearance of the hydrogen absorption lines in the ultra-violet has been

ascribed by B owland to excessive diffuseness or widening of these lines, and if

this view is correct it follows, as Sir W illiam H uggins has pointed out, “ th a t the

hydrogen absorption in the sun must be restricted to a narrow region low down and

close upon the photosphere itself,”f the hydrogen in the higher regions contributing

little or nothing to the absorption.

This view, however, which seems to imply the complete independence between

* R unge and P asciien, “ On the Spectrum of Cleveite Gas,” *Astro.-Physical Jo u rn a l/ vol. 3, No. 1 (1896).
t ‘ An Atlas of Representative Stellar Spectra/ p. 150.

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OF SPECTRA AT THE SOLAR ECLIPSE OF JANUARY 22, 1898.

401

the emission and absorption lines in the sun, is extremely difficult to reconcile

with the ordinary appearance of the lines C and F at the sun’s limb. W ith a radial

slit the emission lines are seen to correspond exactly both in width and in absolute

intensity with the dark lines, and it is difficult to avoid the conclusion th a t the

whole depth of the chromosphere is effective in producing the absorption.#

The progressive diminution of intensity of the emission lines in passing from

the visible spectrum towards the ultra-violet appears to be in itself sufficient

to account for the disappearance of absorption beyond H. The total quantity of

hydrogen above the photosphere is probably too small to produce appreciable absorp­

tion when the lines have a certain limiting intensity, although the same lines when

viewed at the sun’s limb may be strikingly conspicuous, chiefly by reason of the wide

diffusion of the gas as already explained in the case of the metallic lines in the flash

spectrum, and also on account of the enormous depth of radiating gas through which

the line of sight passes.

Unlike helium, hydrogen is very conspicuous in the lower chromosphere, and the

fainter more refrangible lines are much more strongly impressed in the photographs

obtained near the times of the two internal contacts than in those taken near mid­

eclipse with much longer exposures. The intensity of the lines evidently increases

rapidly towards the photosphere, but they still remain narrow and well defined even

within

1"of the photosphere.

The Corona Spectrum.

Although the continuous spectrum of the corona is strongly shown on most of the plates exposed during totality, the green line is the only one of which it was possible to obtain measures. The faint line near H in Spectrum No. 6 becomes quite invisible under the microscope, and the new line in the extreme ultra-violet, shown in No. 5, was not discovered until some time after making the measures ; the wave-length of this line was estimated by superposing No. 5 spectrum upon No. 3, the hydrogen lines and H and K being made coincident; the position of the new line was then obtained with reference to the fine lines of the flash spectrum, f
The following are the wave-lengths obtained for the green line which was measuied
on negatives No. 3 and No. 7 :—

No. 3 spectrum X = 5307'0

No. 7 „

= 5299-7

Mean X = 5303*3

* The same may be said of the calcium lines H and K. In the upper chromosphere these lines are narrow and well defined, and correspond exactly with the narrow dark lines at the centres of the broad

absorption lines. t I t is impossible in the reproductions to show the corona lines here mentioned, except the green line.

VOL. CX CVII.— A.

3 F

402

.MR. J. EVERSHED ON WAVE-LENGTH DETERMINATIONS, ETC.,

This result is in satisfactory agreement with the value found by Mr. F owler on the plates obtained by Sir N orman Lockyer. The difference between the two measures above is due to the opposite displacement of the line in the photographs taken at second and third contacts, the point measured being situated about 2' above the moon’s limb. This apparent displacement affects all lines of a diffuse character where the moon’s limb is not well defined.
The three corona lines shown on these plates are therefore—
1. 3388. 2. Near H (on less refrangible side). 3. 5303-3.

The ultra-violet line is similar to the green line in distribution round the limb, and is probably due to the same substance, whilst the line near H differs from the others in showing no maxima of intensity, the substance producing it being evenly dis­ tributed on the west limb.
There is no trace whatever of any other coronal line on any of the plates.

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Summary oe E esults.
The principal results obtained from the study of these photographs are stated briefly in the following paragraphs :—
1. Practically every strong dark line in the solar spectrum is present as a bright line in the flash spectrum.
2. Almost all the flash-spectrum lines (excepting those due to hydrogen and helium) coincide with dark lines in the solar spectrum.
3. The relative intensities of the lines of any one element in the flash spectrum are practically the same as those of the same element in the solar spectrum.
4. The relative intensities between groups of lines belonging to different elements are widely different in the flash and in the solar spectrum.
5. The apparent intensity of the radiation from any element in the lower chromo­ sphere is determined by the extent to which th at element is diffused above the photosphere ; and the real relative intensities between the different elements cannot be judged in photographs of the flash spectrum.
6. The flash spectrum may be considered to represent the upper more extensively diffused portion of a stratum of gas which, by its absorption, gives the Fraunhofer dark-line spectrum.
7. Nearly all of the known metals having atomic weights less than 60 are repre­ sented in these spectra, and no element having a higher atomic weight than 92 is certainly represented.
8. All the strong lines in the flash spectrum can be identified with known elements, and the small proportion of unidentified lines are weak lines.

OF SPECTRA AT THE SOLAR ECLIPSE OF JANUARY 22, 1898.

403

9. The wave-lengths of the hydrogen lines in the ultra-violet agree closely with those derived from Balmer’s formula.
10. The prominences and lower chromosphere emit a strong continuous spectrum in the ultra-violet, beginning near the limit of the hydrogen lines and extending indefinitely in the more refrangible region.
11. The ultra-violet hydrogen lines increase in intensity towards the photosphere, but remain narrow lines in the flash-spectrum layer.
12. Some of the helium lines decrease in intensity towards the photosphere, others increase.

In conclusion,_J have to acknowledge my indebtedness to Dr. B ambaut for much valuable help and advice in the preparation of this paper, and for the kind interest he has taken in the work throughout.
I have also to acknowledge the great assistance rendered to me by Mr. L. E. J ewell, of the Johns Hopkins University, who made a careful and exhaustive study of some positive copies of my plates.
In identifying the lines given in the tables, I have been guided almost entirely by his re su lts; and I am also indebted to him for supplying me with revised values of many of the solar lines given in the last column of each table.

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Table I.—Flash Spectrum Wave-lengths compared ivith the Dark Lines of the Solar Spectrum.

In this table the wave-lengths deduced from the measures of No. 3 and No. 7

spectra are entered in the first two columns. The third column gives the photographic

intensities for No. 3 spectrum. These were estimated on a scale ranging from 1 to 10 ;

1 representing very weak lines, and 10 representing the strongest lines in the spectrum.

Very faint traces of lines difficult to measure are designated 0 in this column.

In column 5 the wave-lengths of the solar lines are given with which the bright

lines have been identified with a greater or less degree of probability. The intensi­

ties as given by Howland are entered in column 6, and the element corresponding

to the solar line in the last column. The wave-lengths of the helium lines are placed

within b rack ets; they are taken from the tables of B unge and P aschen.

The columns 5, 6, and 7 are taken from B owland’s tables of solar lines

published in the ‘ Astro-Physical Journal ’ for 1895, 1896, and 1897, and supplemented

by more recent determinations supplied to me by Mr. J ewell. In a few instances the

identifications and intensities will be found to differ from those given in the tables.

In column 4 an (S) means a sharply defined line, well identified, and suitable to be

taken as a standard line in wave-length determinations. A (?) in this column

indicates th at the identification with the solar line is extremely doubtful.

In the last column a ? means th at the element in question has not been identified

with certainty with the solar line.

3 F 2

404

MR. J EVERSHED ON WAVE-LENGTH DETERMINATIONS, ETC.,

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Table I.

Wave-lengths in hash Photo-

spectra.

graphic

intensity.

No. 3.

No. 7. No. 3.

Character. No. 3.

Wave­

length, £

4^

solar

g

£

spectrum. js R owland. hcH

1 a

3342-3

47-0

—

49-4

—

54*0

58-5

__

61-4

—

68-3

—

73-0

—

80-4

__

84-0

—

88 *1

—

92 *i

—

94-7

—

99-3

3403-45

—

05-17

—

07-32

—

08-97

—

10-24

—

13-0 1

—

15-01

—

2 1 - 42 2 2 - 94 _

25-46

—

26-97

—

28-73

30-61

—

33-54

—

38-40

—

40-93

—

42-24 44-39 46 •34 52-86 56-55 58-58 i 60-53

3442-1 —
53*3 —
60-4

61-68

61-7

63-05

—

64-32

__

65-87

—

2

J3342-062 7 l 42-358 3

0

(One measure o n ly )............................ t

/ 46-882 l 47-066

5 2

4

L o n g ................................................. (S) 49-558 12

Faintly e x t e n d e d ........................... l }

53-875 4 58-649 4

H L o n g ............................................

(S) 61-327 12

3

L o n g ......................................

/ 68-193 5 \ 68-319 1

4

L o n g .................................

3

S h o r t ...........................................

(S) 72-948 12

f 80-424

6

l 80-722 1 6

4

L o n g ...........................

(S) 83-892 10

3

L o n g .................................

(S) 87-988 5

(One measure o n ly )...........................

92-109 2

3

L o n g .................................

'(S) 94-716 6

1

S h o r t ......................................

/ 99-376 2

* • \ 99-489

3

3

Faintly e x t e n d e d ........................... (S) 3403-404

3

1

S h o r t .................................

05-217 2

1

Short . .................................

.(?) 07-597 4

3

Long .

...................................... (S) 08-911

3

1

Visible on south side only . . .

—

—

0

N ot m easured; w-1 estimated . .

__

__

1

Visible on south side only

, , 14-911 15

H\ Equal p a ir ; l o n s r ......................

(S)

H J

(S)

0 1

00 Jr One measure o nly; very short . . • •

1

S h o r t ...........................

2 1 - 353 4

2 2 - 892 4

__

__

—

—

30-671

1

4

L o n g ......................%. .

2

S h o r t ......................

/ 33-453 3 \ 33-715 8
38-376 2

3

Faintly extended . . . . .

f 40-762 20 \ 41-155 15

4

Long . . . .

(S)

3

Faintly e x t e n d e d ........................... (S)

Ill defined . 5 }

42-112 6 44-467 4 46-406 15 53-039 6

Ill defined; short . . . .

i}

3

L o n g ...........................

56-528 3

.

58-601 8

(S) 60-460 4

2

Faintly extended . . . .

1

Interrupted; very short . . . .

f 61-633 5 \ 61-801 8
62-950 6

1

ditto ditto

....

f 64-275 1 \ 64-608 1

2

Very faintly extended

....

f 65-900 • • \ 66-015

4 6

Ti Fe Ti
Ti Co Ti Sc Cr Cr ? Cr Mn Ti Ti Ni Ti Ti Zr Ti Fe Zr Fe Cr Co Fe Cr — __
Ni Cr Cr | __ |
Zr Cr Ni Zr Fe Fe Mn Ti Ni Ni Ti Ni Mn Ti Ni Co : Fe Sr 1 Co | Fe i

OF SPECTRA AT THE SOLAR ECLIPSE OF JANUARY 22, 1898.

405

Table I.—continued.

Downloaded from https://royalsocietypublishing.org/ on 14 March 2024

Wave-lengths in flash Photo-

spectra.

graphic

intensity.

No. 3.

No. 7. No. 3.

Character. No. 3.

Wave­

length,

&

solar

g

+£5

spectrum.

s<D

Rowland. £

r---- 1

3467-46 68-72 717274-28 75-67 77-26 79-48 81-20 83-08 88-85 91-16

— 36 — 58
3474-26 — 77-31 —
83-02 88-84 91-10

93-22 94-60

93-21 _

96-17

96-11

97-82
99-14 3500•45
02-30 05-06 10-96 13-95 ! 15-15 17-37 20-26 21-44 21-84

97-71 __ __ __ 3505-01 11-10
15-40
—

24-67 26-22 26-59 30-80
31-83
33-35 35-64 414245-25

24-72
30-93
—
35-68 17 24
45-39

48-08

—

49-07

51-93

_

53-15

53*87

5 5 - 02\ __

5 6 - 82 56*94

Ob 1)1

KQ . AQ DO DO

; 60-88

i 61-82

0

Stronger south than north of centre • 0 )

__

__

0

D i t t o .................................................

3468-821 2

; } Equal pair, short and interrupted . .

f 71-404 t 72-680

3 5

3

L o n g ................................................. (S) 74-287 2

2

S h o r t .................................................

75-594 10

3

L o n g ................................................. .

77-323 5

H \ Ill defined ; s h o r t ........................... • • H J

79-531 81-302

2 2

3 3

1 l

L o n g .................................................

(S) (S)

83-047 88-817

5 4

3 J A very faint line is visible about A 3490 ±

91-195

5

2

111 defined; faintly extended . .

93-114 10

1

S h o r t ................................................. •CO 94-815

2

/ 95-853 2

3 . L o n g ................................................. •(*) t 95-974

2

2

S h o r t ......................................

/ 97-668 3 \ 97-982 8

0

I n t e r r u p t e d ...................................... •CO

1

S h o r t .................................................

0

Short (one measure only) . . . .

35 \ Long equal p a i r ................................. H J

(S) •(S)

2

S h o r t .................................................

22 1J Faintly e x t e n d e d ........................... (S)

r } S h o r t ............................................................

1

On continuous spectrum north of centre

99-248 0 3500-474 3
02-394 3 05-036 5 10-985 5 13-965 7 15-206 12 17-446 3 2 0 - 397 2 21- 410 8 21-748 4

only

3I

L o n g ................................................. .(S)

24-677 20 26-183 6

Close pair very s h o r t ......................

1 }

1

Faintly e x t e n d e d ...........................

30-919 3 / 31-982 3

1

S h o r t ................................................. -(*) \ 32-143 4

0 3

S h o r t .................................................

33-345 6

Faintly e x t e n d e d ........................... .(S) 35-554 4

41-237 7

Short, fine l i n e s ................................

1 }

2

Faintly e x t e n d e d ...........................

42-232 6
45•336 2 f 47-941 5

1

I n t e r r u p t e d ...................................... • • 48-175 L 48-332

3 5

49-151 2

l

S h o r t ................................................. }

•co

0

1

On continuous spectrum . . .

22~ 1 2 f

Faintly e x t e n d e d ...........................

0

Invisible to north s id e ..................... •CO

1

52-098, 1
55- 079 9 56- 738 2 58-672 8 61-037 4 61-898 3

__
Fe Fe, Zr
Ni Mn Fe Ti Zr Zr Mn Mn Ti
Ni
Fe Ti Mn Mn Fe Ti Ti Co Ti Ti Fe Ni V Ti Fe Co
Ni Fe
V Mn Mn Fe Ti Fe Fe Y Mn Mn Mn, Ni Y 1 Zr
Fe Zr Fe Co Ni !

406

MR. J. EYERSHED ON WAVE-LENGTH DETERMINATIONS, ETC.,

Table I.—continued.

Wave-lengths in flash Poto-

spectra.

graphic

intensity.

No. 3.

No. 7. No. 3.

Character. No. 3.

Wave­

length,

solar

• grH

C£D

spectrum. o R owland. 1—'S1

r-CBHD W

Downloaded from https://royalsocietypublishing.org/ on 14 March 2024

3565-52 66-25 67-77 70-21 72-61 73-75 76-51 78-76 81-16 84-37

3565-64 —
68-08 70-24 72-63 73-98 76-52 78-88 81-37 —

85-45 87-08 87-71

85-46
—
87-51

899092-07 93-55 94-81 96-05 97-72 3600-71 01-90 03-67 05-35 06-48 08-98 11-05 13-91
18-98
21-26 21-62 23-45 24-86 28-71

72 — 43
— 93*84 — 96*39 — 99*59 — 3603*97 05*64 — 09*00 — 14*00
19*01
— — — 25*02 —

30 •85 31-50 33-11

— 31*37
—

34-19

34*54

353641-32
42-70
45 •35 47-86 49-86

11 — • 50
41-65
42-81
—
47-77

2 ]

1 |

2 l Long lines......................................

2J 1

2+ J

1

S h o r t ............................................

3565-535 20
66-522 10 67-835 4
(S) 70-273 20 72-676 6 73-874 3

3 1 2 \ L o n g ............................................ • .(8)

3 J

1

More distinct in clear spaces than on con-

76-527 3

78-832 10

81-349 30

—

—

tinuous spectra.

85-479 7

i

87-130 8

0

Difficult to m easure; visible only on con- 87-370 7

tinuous spectrum on north side. 0 )

Very faintly extended - * • 5 }

i 89-773 5 90-509 2

2

F aintly e x t e n d e d ...................... . . ( « )

92-169

2

2

L o n g ............................................ . .(S) 93-636 9

1

S h o r t ............................................

94-784 6

2

L o n g ............................................

96-195 4

1

S h o r t ............................................

97-854 8

2 i F aintly e x t e n d e d ......................

3600-880 3

2 1 S h o r t ............................................ 1 /

(?) 02-060

1

03-922 3

2

L o n g ............................................ . .(S) 05-479

7

0 2

S h o r t ........................................... L o n g ............................................

• • (?) • .(S)

06-838 6 09-008 20

2

S h o r t ............................................

11-189 2

H Narrow strong line with shading. Long 13-947 4

3

Probable double (width •92).

.

. Long

f \

18-919 19-539

20 8

1

S h o r t ............................................

21-244 3

1

S h o r t ............................................

21-612 6

0

Very s h o r t .................................

23-362 5

21 Faintly e x t e n d e d ......................

, , 24-979

5

1

Fine and sharp on continuous spectrum ; f 28-847

2

does not extend beyond

\ 28-967 2

22 \ L o n g ...........................................

2 J

2

Very fine and distinct; ends abruptly at

30-876 4 31-605 15 33-277 2

sides of continuous spectrum

1

L o n g; almost invisible upon continuous (3634-393) —

spectrum

° 1 Very short on continuous spectrum only 0 J

22 Long, sharply defined . . . . • .(S)

3

/

JJ

??••••

\

2

Very faintly ext ended. . . .

35- 091 3 3 6 - 608 4 41-473 4 42-820 7 42-912 2 45-475 3

2

L o n g ........................................... • .(S) 47-988 12

1

Short; stronger on continuous spectrum (?) 49•654 5

Fe Ni ?
Fe Sc Ti Sc Cr Fe —
Fe Fe Co
1
C V? Cr Fe Ti Ni Y Y Cr ? Cr Fe Fe Y Sc Fe Ni ? Fe Fe Ti Y La Ca ? Fe Y
He
Ni Cr ? Ti Ti Sc Sc? Fe ! La

OF SPECTRA AT THE SOLAR ECLIPSE OF JANUARY 22, 1898.

407

Table I.—continued.

Wave-lengths in flash Photo-

spectra.

graphic

intensity.

No. 3.

No. 7. No. 3.

Character. No. 3.

Wave­

length,

solar

£

<£D

spectrum.

1

Rowland. A

Downloaded from https://royalsocietypublishing.org/ on 14 March 2024

3651-65 —
55-78

3652-46 — —

59-58

—

61-16

—

62-14

—

63-40 64-71 66-15 67-70 69-52 71-45 73-77 76-32

63-42 64-67 66-07 67-65 69-54 71-58 73-80 76-50

77-64

78-6

79-41 82-80 85-28 86-98 89-48 91-67 93-83 97-26 3703-87
05-92
| 07-66 09-09
! 10-14 12-10
15-32
18-10 19-82 22-05 24-48 27-40 34-55 36-94 39-11
41-51
43-26

79-43 82-82 85-17 86-81
— 91-67 __ 97-20 3703-85
— _ | __ __ 12-00
—
__ 19-96 21-89 __ 27-64 34-54 37-18
—
41-83
43-31

45-58
48-01 50-29 57-57

45-69
_ 50-18

2 ~

\ /

Very faintly extended, a line at 3653 •4 ± f 3651-614

just v isib le...................................... (?) \

51-940

1

Very short; stronger on continuous 55-801

spectrum

2

Faintly e x t e n d e d .................................(?

59-663

1

In clear spaces on south side only . . .

—

2

Probably a line superposed on hydro- 62-378

1 ] 2 2

gen line

2j 21

►Long lines, not very sharply defined .

.

—

3

3

3

f 77-764

2

Short; narrower than hydrogen lines (?) .< 77-831

L 77-991

3J Probably a Fe line on less refrangible side

—

3

L o n g ...........................................................

—

5

Very long; well d e fin e d ......................(S) 85-339

3|~ L o n g ...........................................................

0

S hort; in terru p te d .................................(?)

— 89-614

H L o n g ...................................................... •

—

i

S h o r t ............................................................

—

Long. A very faint line is visible half­ —

4 j j way between Ho and H£ A3701 ±

3

Faintly e x t e n d e d ................................

3705-708 06-175

0 nL Very short; interupted; not visible (?)

1 ] on continuous spectrum

(?)

2

S h o r t ......................................................(?)

07-702 0 9 •389 10-431

4

L o n g ...........................................................

/ 15-319

2

Very faintly extended................................ \ 15-615

0

On continuous spectrum oidy.

—

3

Long, very sharply defined . . . (S) 20-084

n

L o n g ...........................................................

—

i

Very short, continuous spectrum only . 24-526

21 S h o r t ................................................ (•)

27-778

4£ 3J

Narrower on continuous spectrum . . . Long . ......................................................

— 37-281

0

S h o r t ...........................................................

r 41-205

3

L o n g ........................................................... \ 41-791

1

Short, very narrow l i n e ..........................................................

43-508

f 45-401

3

L o n g ...............................................................................................................................

45-717

L 46-058

1

F a in tly extended, n a r r o w ..............................................

48-408

4 i Narrower on continuous spectrum

2

Ill-defined, short 0 ) ................................................................................

—
57-824

7 Fe

4 Sc

3

?

5 : Fe

—

Uu

5 Ti, H 30

H 29

h 28

H 2r

— J

Hco Hi/'

HX H 4> Hr 5 Fe 3 Cr 3 Cr

—

Hr

—

Hcr

10 Ti

— Up

6 Fe

— II7T

—

— Ho

H^

9 Fe

6 Ca?

2 Ti

8 Fe

3Y

Hr

0 A Cr?

4 y?

—

— 1

40 Fe

— H/x

6 Fe

4

JT7b1 e

—

Ha

30 Fe

4 Ti

4 Ti

6 Fe

2 Co

8 Fe

6 Fe

10

Fe

O' LLK

4 | Or 'i r, r1p1*

408

MR. J. EVERSHED ON WAVE-LENGTH DETERMINATIONS, ETC.

Table I.—

con

Wave-lengths in flash Photo-

spectra.

graphic

intensity.

No. 3.

No. 7. No. 3.

Character. No. 3.

Wave­

length,

&

solar

spectrum. O Rowland. h£H

|
AOC 1 3

Downloaded from https://royalsocietypublishing.org/ on 14 March 2024

3759-32 61-46 63-66 66-84 70-77 74-03 75-79 83-28 86-6± 88-53 90-0± 94-72 97-98

3759-34 61-25
— —
70-77
—
— —
—
89-57
— —
98-07

3805-19 \

07-46J

—

12-79

—

14-22

—

15-70 3815-92

20-23

20-17

2 4 - 16 2 4 -

2 5 - 51 2 5 -

27-4 ±

—

29-32

29-28

32-13

32-06

35-58

35-14

38-36

38-32

40-61

—

49-94

—

56-21

56-36

59-96

60-00

72-09

73-1

78-29

78-7

82-75

—

89-34 I 89-1

95-29

—

3900-25 3900-7

06-11

—

13-55

13-6

19-90

22-23

22-8

27-52

—

34-4

33-1

44-0

44-4

50-1 ±

—

56-9

61-6

—

69-8

68-3

82-6 90-6 98-8

83-6
—
—

4 H

! J

Very long, well defined . . . Longer than Hi, and narrower .

. .

(8) 3759-447 (S) 61-464

12 7

Ti Ti

H Long, faint, visible on continuous .

63-945 10 Fe

i

Long, faint, not visible on continuous. . 67-341 8 Fe

6

Narrower on continuous spectrum . .

—

—

Hi j

S h o r t .................................

74-473 3 Y !

0

Very s h o r t .......................................

75-717 7 Ni 1

1

S h o r t .................................................

83-674 6 Ni 1

0

Short (wave-length estimated) .

/ 88-046 8 Fe

2

S h o r t ................................................. ■(*) \ 88-839

2 Y1

0

Short (wave-length estimated).

0

Shoi’t ...............................................................

95-147

8 Fe

7

Diffuse outside, narrower on continuous

—

H0 j

spectrum.

0

Trace of lines or band, poorly defined

3805-486 6 Fe 07-681 6 Fe

2

F aintly e x t e n d e d ...................................

1

S h o r t .................................................

14-698 8 Fe?

2

F ain tly e x t e n d e d ...................................

15-987 15 Fe

3

Long, nearly equal to H r;. . .

(8)

91 73 5

Ill-defined pair, faintly extended }

.

0

(Wave-length estimated) . .

20-586 25

24-591 6

26-027 20

—

—

Fe Fe ! Fe
—

3 1

(8)

29-501 10

Mg

3 j Long, nearly equal to H r; . . .

32-450 15 M g

7

—

—

H r;

3

Long, nearly equal to H r; . . . (8)

38-435 25

Mg

1

S h o r t ...............................................................

40-580 8 Fe

1

Short, h a z y .................................................

' I 50-118 10 Fe !

2

L o n g .................................- . .

56-524 8 Fe

3

Long . . ...................................... (S) 60-055 20 Fe !

1

Ill-defined, wide, faintly extended . • 0 ) 72-639

6 Fe

2

L o n g ..............................................................

/ 78-152 8 Fe

1

Ill-defined s h o r t ..........................................

t 78-720 7 Fe

8

Narrower on continuous spectrum .

—

—

H t

2

F aintly e x t e n d e d ...................................

* 95-803

7

Fe

3

Long(Ti is the predominating element) (S) 3900-681 5 (Fe?)Ti

1

vVide, short, probably two lines

• (?)

05-660 12

Si

3

Long (Ti is the predominating element) (S) 13-609 5 Ti(Fe) ;

1 I

(?)

1 [ S h o r t ..............................................................

20-410 10

Fe !

1 J

10

(K) width of line 2 -9 5 ............................

33-825 1000 Ca !

22

F aintly e x t e n d e d ................................... (8)

44-160 15

A1

1

Centre of group ...................................

50-102 5 Fe

1

D i t t o ..............................................................

f 56-476 \ 56-819

4 Co, Ti 6 Fe

3

L o n g .............................................................. (8)

61-674 20

A1

150 J\ (H) width of line 3-92............................

f \

68-625 70-177

1 700
J

Ca
Pie

1

S h o r t .............................................................. (?)

82-742

3

Y

1

S h o r t ............................

. .

1

Group of l i n e s .................................

—

__

j 98-790 j 4 Ti i

OF SPECTRA AT THE SOLAR ECLIPSE OF JANUARY 22, 1898,

409

Table I.—continued.

Wave-lengths in flash Photo-

spectra.

graphic

ntensity.

No. 3.

No. 7. No. 3.

Character. No. 3.

Wave­

length, &

solar spectrum.

1 J

Rowland. £

4£^ ,—a<v1 W

Downloaded from https://royalsocietypublishing.org/ on 14 March 2024

4005-5

12-7

—

26-56 4026-8

30-7 1

—

34-4 J

46-3

46-5

54-7

54-1

63-9

63-7

72-1

78-3

78-1

4102-5 4102-4

09-9

—

18-9 \ \ 23-6 J 28-0 1

21-4 { —

33-9 J

43 -4

—

63-6 72-9 77 -7 4216-3 26-9

....
4215-8 27-0

33-3

—

47-5 54-8 60-4 73-6 90-2 97-1

46-7
__ 74*5 91-7
—

4300-5 4300-9

08-2
13-7 21-3 26-1 41-4
51-7
58-7 75-2 DQ OQ , 0(*
95-5

— 15-1
41-3
— —
—
95-2

1

S h o r t .................................................

1

D i t t o .................................................

3

Long, not visible upon continuous .

2 J i Groups of short l i n e s ......................
H Long, visible across continuous . .
i

Faintly e x t e n d e d ...........................

i }

4

L o n g .................................................

7

Very diffuse on violet side . . .

1 , Group of faint l i n e s ......................
1 }
Very faint group. 1 } 9 i Probable d o u b le................................. 2 1 Visible on c o n tin u o u s...................... 0

0u0 ]J>1 Ill-defined,

4

L o n g .................................................

3 1

L o n g ................................................. 2 r

3 J 2

1

2

Probably a group of lines.

2 i

1

Probably faintly extended.

2

--

2

( G ) ......................................................................................................

1 > Faintly extended lin es.....................

1

2

7

Best defined on red side . . . .

2

S h o r t ................................................

1

2^2 )JI Faintly e x t e n d e d ...........................

2

L o n g ................................................

4005-408 7

12-541 4

(4026-342) —

30-918 10

33-224 8

(S) 45-975 30

—

—

(S) 63-759 20

•(S) 71-908 15

(S) 77-885 8

4102-000 40

—

—

• 0)

23-384 12

—

—

. (4143-919) —

44-038 15

63-818 4

•CO 72-923

4

(S) 4215-703 5 26-904 20
f 33-328 ' 4 \ 33-772 6 •(0 46-996 5
54-505 8 60-640 8

91-114 3

(4300-211 3 j 00-732 2 J 07-907 3 \ 08-081 6
15-138 3 20-907 3 25-939 8 40-634 20 f 51-216 3 L 51-930 5

75-103 2 83-720 15
f 95-201 3 \ 95-413 2

4400-6 05-4 16-8 26-4 35-7 44-1 50-4

—

4417-0
—

43-8

)

—

Very difficult...................................... s} 1 0
uA
2
1 o

—

—

4435-851 4 43-976 5

VOL, CXCVIL — A.

Fe Ti He Mn Mn Fe
—
Fe Fe Sr HS —
La
—
He Fe Ti Fe
Sr Ca Fe Fe Sc 1 Cr Fe
Ti
Ti Ti Ca Fe Ti Sc Fe
Hy
Cr Cr
V, Mn Fe Ti
V, Zr
—
Ca Ti

410

MR. J. EVERSHED ON WAVE-LENGTH DETERMINATIONS, ETC.

Table I.—continued.

Wave-lengths in flash Photo-

spectra.

graphic

intensity.

No. 3.

No. 7. No. 3.

Character. No. 3.

Wave­

length,

£

solar

•g

•<£6D

spectrum.

1

Rowland. £

Downloaded from https://royalsocietypublishing.org/ on 14 March 2024

4455-3

—

72-0 82-0 90-8 4501-6 09-3 15-9 23-2 34-9 51-6 55-2 62-0 66-0 69-9 74-0 87-7 90-7 4629-4 46-6 68-0 85-6 4713-2 4805•3 25-0 60-3 4922-0 33-5 57-4 5017-4 5164-7 \ 73-0 J 83-5

4472-1 --—
4501-6 — —
—
34-5 46-0 55-0
65-0 }
72-9 } 88-4 —
—
—
—
86 *3 4713*4
— — 4860*9 — 4930*2 — 5016*1 5167*3 1 74*7 J 83*9

5205•3

—

27-7 35-1 70-0 5307-0* 15-4 26-5 35-5 5876-0
93-7
—

—
— —
5299 *7*
— —
— 5875*9
—■ 6563*0

0

—

——

r Long, well-defined on R side, very diffuse "1

3 < on B side, weak over continuous spec- > (4471-646) — He

o 1 tr u m .......................................................

0

—

—

—

2

4501-448

5

Ti

0

—

—

—

0

—

——

0

—

——

2

34-953

4

Ti

2

—

——

2

55-662

3

Ti

2

Group of lines, faintly extended.

2

Ditto.

1

—

——

0

—

——

1

4629-521 6 Ti, Co

0

46•347 5 Cr

0

—

——

0

—.

— , __

2

Long, not visible on continuous spectrum (4713-252) —

He

0

—

——

0

—

——

5

4861-527 30 H p

2

Visible across continuous spectrum. . . (4922-096) —

He

2

—

—. —

0

Very difficult.

—

——

2

Visible across continuous spectrum. . . (5015-732) — He

(b” V " W ) L o n g ........................... | 3 }

5167-497 15 72-850 20

Mg Mg

3

O') L o n g .................................................

83-791 30 Mg

f 1 i

5204-680 5

Cr

06-215 5 Cr

1 0

08-596 5 Cr

—

__

0

—

—

__

0

—

__ __

1

Very diffuse (corona line).

1

(1474 K ) ...................................................... 5316-790 4

Fe

0

—

—

—

0

—

—

—

5

o n ............................................................ (5875-870)

He

2

P '> D " ) ..................................................{

5890-186 96-357

30 20

Na Na

(C) strong on No. 7 p la te ........................... 6563-045 40 H a

* Apparent centre of line displaced to red at second contact, and to blue at third contact. Mean
position = 5303 •3.

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Intensity. Intensity. Element.

OF SPECTRA AT THE SOLAR ECLIPSE OF JANUARY 22, 1898.

411

Table II. — Spectrum o f Prominence.
The wave-lengtns given in the first column of this table are deduced from measures of the images of a very small bright prominence in spectrum No. 4. This prominence was situated almost at the point of second contact at position angle 59° (solar latitude + 23°).
The photograph was exposed at the beginning of totality immediately after the disappearance of the flash spectrum.
The prominence images are well defined circular spots in all radiations except the calcium and brighter hydrogen rays, which show wings due to motion in the line of sight.
The columns of this table are arranged as in Table I., and the intensities in column 2 were estimated in the same way as those of No. 3 spectrum given in Table I.
The helium wave-lengths given within brackets in column 4 are from R u n g e and Paschen.
Table II.

W ave-length No. 4
spectrum.

Remarks.

Wave-length, solar
spectrum.
R ow land.

3435
3534 J 3537 \ 3614-0 3618-9 3625-3 3631-6 3634-6 3668 ±
3669-52 3671-61 3673-92 3676-55 3679-55 3683-06 3685• 34 3687-12 3691-75 3697-18 3704-11 3705-86 3712-19 3720-02 3722-07 3734-52 3737-27
3741-79

Limit to which continuous spectrum of pro­

minence can he traced

Continuous spectrum is much brighter at 3535*554

4

this point

0

3613*947

4

0

3618*919 20

0

One measure o n l y ........................................... 3624*979

5

1

3631*605 15

1

......................... .....

(3634*393) —

—

Beginning of continuous spectrum in promi­

—

—

nences

0 0

1

R ather difficult to m easu re................................

— —

— —

0

Silver deposit very w e a k ................................

—

—

0 „

—

—

1 ]

—

—

1

—

—

3

3685*339 10

1

—

1

.................................................................................

—•

—
—

1

.................................................................................

—

—

1

—

—•

1 > Well-defined and very small circular d o ts. 2

3705 *708

9

—

—

1 2 2

3720*084 40

................................................................................. /

—
—

—
—

1

.

3737*281 30

i

f 3741*205

4

1 !\

[3741*791

4

3 g 2

Ti
Sc Fe Ti Fe He —
Hip
HX
H</>
Hu Hr
Her
Ti Hp
H it
Ho H£ Fe Hr Fe H/x HA. Fe Ti Ti

412

MR. J. EVERSHED ON WAVE-LENGTH DETERMINATIONS, ETC.,

Table II.—continued.

Downloaded from https://royalsocietypublishing.org/ on 14 March 2024
Intensity.

AYave-length No. 4
spectrum.

tA
§ S
WH

Remarks.

Wave-length,

solar

S

spectrum.

o1

R owland.

s

3745-98
3748-47 3750-21 3759-53 3761-40 3770-80 3798-12 3820-09 3825-77 3829-39 3832-56 3835-63 3838-56 3860-14 3889-09 3900-5
3913-2
3933-8 (3944-0) 3968-6 4026-3 4077-8 4102-2
4215-7 4340-6 4471-8 4713-1 4861-5

■s
1

f 3745-717

8

\ 3746-058

6

0

3748-408 10

2

—

—

2 > Well-defined and very small d o ts ...................... 3759-447

12

2

3761-464

7

2

—

—

3

................................................................. .....

—

—

1 0

1 J>

N ot well d e f i n e d .................................................

f 3820-586 \ 3826-027

25 20

0 ' , ...

................................................. 3829-501

10

1

3832-450 15

3

—

-— -

2

Well-defined nearly circular d o ts ...................... 3838-435 25

1 ►Slightly w i n g e d ................................................. 3860-055 20

4

—

-— -

0

. . . .................................................................. 3900-681

5

0

3913-609

5

10

K, triangular black s p o t ................................. 3933-825 1000

0

Not measured wave-length in No. 3 spectrum 3944-160 15

10

H, triangular black s p o t ................................. 3968-625 700

Fairly good d e f i n i t i o n ................................. 5 }

(4026-342)

4077-885

8

5

Circular black spot with wings due to motion 4102-000 40

in line of sight

2

4215-703

5

5

Same as H S ............................................................ 4340-634 20

3

AVell-defined s p o t ................................................. (4471-646) —

1

(4713-252)

5

Circular spot slightly w in g e d ........................... 4861-527 30

Fe Fe Fe H K Ti Ti Hi H0 Fe Fe Mg Mg Ev Mg Fe H£
Ti(£v)
Ti(Fe) Ca A1 Ca He Sr HS
Sr Hy He He
E/ 3

OF SPECTRA AT THE SOLAR ECLIPSE OF JANUARY 22, 1898.

413

Downloaded from https://royalsocietypublishing.org/ on 14 March 2024 0 1 Q

Table III.—Hydrogen Lines.

1

Designation.

Spectrum No. 3.

Spectrum No. 4.

Mean of 3 and 4.

Computed.

CL
P y
8
€
c
V
0
i
K
X
/X
V
£ 0
77*
p
O’
r
V
cp
Ay xTp (0
27*
28 29 30 31
CO
1

_
4860-3 4341-4 4102-5
Obscured 3889-34 3835-58 3797-98 3770-77 3750-29 3734-55 3722-05 3712-10 3703-87 3697-26 3691-67 3686-98 3682-80 3679-41 3676-32 3673-77 3671-45 3669-52 3667-70 3666-15 3664-71 3663-40 3662-14 3661-16
Limit

__
4861-5 4340-6 4102-2 by H 3889-09 3835-63 3798-12 3770-80 3750-21 3734-52 3722-07 3712-19 3704-11 3697-18 3691-75 3687-12 3683-06 3679-55 3676-55 3673-92 3671-61 3669-52
_____
_____
____
—
—
—
of series

4860-9 4341-0 4102-3
—
3889-21 3835-60 3798-05 3770-78 3750-25 3734-54 3722-04 3712-14 3703-99 3697-22 3691-71 3687-05 3682-93 3679-48 3676-43 3673-84 3671-53 3669-52 3667-70 3666-15 3664-71 3663-40 3662-14 3661-16 (theoretical)

6563-07 4861-52 4340-63 4101-90 3970-22 3889-20 3835-53 3798-04 3770-77 3750-30 3734-51 3722-08 3712-11 3704-00 3697-29 3691-70 3686-97 3682-95 3679-49 3676-50 3673-90 3671-48 3669-60 3667-82 3666-24 3664-82 3663-54 3662• 40 3661-35 3646-13

* Series number, a = 3.

- -6 + -4 + -4
—
+ -01 + -07 + -01 + -01 - -05 + -03 - -02 + -03 - -01 - -07
+ -o i
+ -08 - -02 - -01 - -07 - -06 + -05 - -08 - -12 - -09 - -11 - -14 - -26 - -19

Spectrum No. 7.
(6563-07) 4860-9 4341-3 4102-4
—
3888-87 3835-05 3797-97 3770-70 3750-15 3734-50 3721-85 3712-05 3703• 86 3697-24 3691-71 3686-75 3682-87 3679-47 3676-53 3673-84 3671-59 3669-54 3667-67 3666-08 3664-68 3663-27
—
—

Evershed.

Phil. Trans., A , vol. Plate 10.

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Fig, 2.

Spectrum No. 1. Artificial cusp.

Spectrum No. 9.
Comparison between cusp spectra photographed during the solar eclipse, and artificial cusp photographed in ordinary daylight—to show the relative faintness of the Fraunhofer lines in the eclipse spectra, and the great extension of the latter in the ultra-violet. (The absence of lines between F and H in each spectrum is due to over-exposure.)

Evershed.

Phil. Trans., A> vol. 1 9 7 , Plate 1 1 .

34

3t5

36 37 313 39 4 0 4 1 4)2 4 3 4 4 45 4 6 47 48 # 5l951l5253M5556575859

I I ill

III

Fig. 1.

Spectrum No. 3.

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Fig. 2.

Spectrum No. 4.

Fig. 3.

Spectrum No. 5.

Fig. 4

Spectrum No. 6.

Fig. 5.

m K H R eH S

He

Spectra photographed during total phase. Eclipse of January 22nd, 1898.

Spectrum No. 7.

Downloaded from https://royalsocietypublishing.org/ on 14 March 2024

Evershed.

Phil. Trans., A , vol. 1 9 7 , Plate 1 2 .