882 
^T?t. J. EVERSHED OX ^YAVE-LEXOTH DETERMIXATIOXS, 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 v’as 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 ultra-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 (A. 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 X 3840. (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 tiuced 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. 
Xumher. 
Exposure times. 
Plate used. 
Spectrum 
photographed. 
Limits of 
wave-length. 
1 
second.a. 
Second contact - 20 (inst.) 
Edwards’ isochromatic 
Cusp 
X. A. 
3.36 to -590 
2 
„ ,, -10 (inst.) 
medium 
Ditto 
Cusp 
340 „ 590 
3 
„ „ - 2 to + 2 
Ditto, instantaneous 
Flash 
334 „ 600 
4 
„ ,,4-8 (inst.) 
Ditto 
Chromosphere 
343 „ 580 
5 
,5 "h 40 to + /5 
Ditto 
Corona 
335 „ 590 
6 
11 + / 6 to -f- 85 
Ditto, snapshot 
r Corona and 
350 ,, 590 
7 
11 11 + 86 to -f-110 
Ditto 
]_ chromosphere 
344 „ 656 
8 
Third contact + 1 (inst.) 
Sandell triple coated 
Flash 
345 „ 530 
9 
„ „ +9 (inst.) 
Ditto 
Cusp 
345 „ 530 
10 
„ ,, -1-19 (inst.) 
Ditto 
Cusp 
345 „ 530 
All tlie expi.)sures 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 X 390 and X 340, but tlie 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- 
