SP. Langley—New method in Solar Spectrum Analysis, 141 
attempting the solution of the problem by means of the sun, 
for the whole displacement due to it, is (as Professor Young 
has remarked in illustration), but one-seventy-seventh of the 
distance between the D lines, or between one-twelfth and one- 
thirteenth of one division of Angstrim’s scale. Zéllner, Secchi 
and Hastings have believed that ‘they, nevertheless, detected a 
change in the refrangibility of the light, and Vogel* using Zéll- 
ner’s reversion spectroscope obtained a displacement of from 
‘08 to 0-15 of one of Angstrém’s units. In August last, Profes- 
sor Young gave the results of his own measurements with one 
of Mr. Rutherfurd’s gratings, showing an equatorial velocity of 
1™42. Professor Young was unable to find any displace- 
ment of the atmospheric lines. This last researcht+ being much 
More systematic than its predecessors, and given in satisfactory 
detail, has turned the weight of scientific opinion in favor of 
. the view, that the change due to motion of the luminous body 
18 fairly proven. It can hardly, however, be deemed superflu- 
ous to still offer upon so important a question, the results of an 
independent method of measurement, and one which renders 
errors from instrumental displacement, on the danger of which. 
so much stress has been deservedly laid, in the sense in which 
the word is here used, not only unlikely but impossible. 
In the course of a research upon the selective absorption of 
the solar atmosphere, I arranged in 1875, means for com 
mee homogeneous lights from different parts of the disc. 
The apparatus was too complex for description here, but 
it consisted essentially, in the provision of two pair of right- 
angled prisms.of total reflection, so disposed in connection with 
4 spectroscope, that the spectra could be formed side by side, 
of light from different parts of the sun, and of a photometric 
“pparatus by which the relative intensity of the lights at differ- 
ent parts of these spectra could be compared. The results of 
this research, with an improved form of the instrument, will I 
Doppler, to which this apparatus is especially applicable. The 
theory of the Daeg sta method is very simple. Let two spectra 
* Beobachtungen auf der Sternwache zu Borhkamp. : 
+ American Journal of Science and Arts, vol. xii, Nov., 1876. 
