176 Prof. J. N. Lockyer. On the [Dec. 13, 



The wave-lengths of some of these lines may also require correction 

 for displacement due to motion in the line of sight, when the condi- 

 tions have been more fully investigated. Attention may be specially 

 directed to two lines at 4384 and 4465 ; in the spectrum of yS-Lyras 

 there are two bright lines with the normal positions 4388 and 4471, 

 agreeing in position with prominent lines in the spectra of stars of 

 Group 1117,* and it seems possible that we have to deal with the 

 same lines in 7-Cassiopeise. This is rendered more probable by the 

 fact, which will appear later, that the two lines in question appear as 

 bright fringes on the more refrangible sides of dark lines, having the 

 wave-lengths 4388 and 4471. 



(3) During the period covered by the photographs there is no evidence 

 of any change in the intensities of the principal bright lines. 



(4) The bright lines of hydrogen are double in all the photographs 

 taken with sufficient dispersion. 



The series of twenty-six photographs, showing the duplicity of the 

 hydrogen lines, was taken with the 6-in. prism of 45, and extends 

 from May 18, 1892, to November 16, 1894. 



[7 and H6 usually show the doubling best, but in some of the 

 photographs H is also clearly seen to be double. The doubling is 

 not so clearly seen at He, probably owing to the presence of other 

 lines near the same wave-length. The double lines are somewhat 

 diffused at both edges. 



(5) There is no evidence of orbital movement during the period which 

 has elapsed since May, 1892. 



Careful measurements of the distance between the two bright lines 

 at [7 and H have been made by Mr, D. Baxandall, and it was 

 found that the distances are constant, within the limits of accuracy 

 in measurement. 



(6) Assuming the presence of two sources of bright hydrogen lines, the 

 relative velocity in the line of sight is about 115 miles per second. 



This velocity has been deduced from measures of the separation of 

 the lines at [7 and H in the photographs taken with the 6-in. prism 

 of 45. 



(7) The bright lines of hydrogen are superposed on broad dark 

 bands. 



This was noted in the earliest photographs, and is fully con- 

 firmed by those subsequently obtained. H/2, 1*7, and H6 exhibit 

 this feature prominently, but the same is occasionally seen at He and 

 H. It has also been noted that C presented the same characteristic 

 when observed by Messrs. Fowler and Sliackleton on October 21, 

 1894. The borders of these dark bands are all ill-defined, but they 

 appear to be symmetrically placed with regard to the bright lines. 

 The dark bands are from 10 to 12 tenth-metres broad. 

 * ' Phil. Trans.,' A, vol. 184, p. 725. 



