Further Observations on Nova Persci. 



135 



The spectrum has undergone great modification since the last photo- 

 graphs were taken at Kensington in March and April. The lines are 

 about the same in number and position, but their nature and relative 

 intensities have vastly changed. In the latter part of March and the 

 early part of April the lines were generally broad and ill-defined. 

 They are now narrower, and with better defined edges. The greatest 

 change noticeable in the spectrum is with respect to the relative 

 weakening of the hydrogen lines generally and the alteration in 

 relative intensity amongst some of them. In the earlier photographs 

 the hydrogen lines were very prominent, and the individual members 

 of the series gradually weakened as the ultra-violet part of the 

 spectrum was approached. In the latest photographs they appear of 

 quite secondary importance. H/2, Hy, and H8 are all present, but 

 occur only as comparatively weak lines, especially the latter two. 

 With regard to He, apparently the only other hydrogen line shown, 

 the case is different. The line at or near the position of He is now 

 about the second strongest line in the whole photographic spectrum, 

 and many times stronger than either H6\ Hy, or H/3. With this fact 

 in view, it may be suggested that this strong line is possibly not 

 wholly due to hydrogen, but is mainly a new line of unknown origin, 

 which happens to fall exactly on, or very near to, the position of He. 

 The line appear.-* to be of much the same nature as the stronger 

 .adjacent line at A 3868. The following table gives the wave-lengths 

 and intensities of the lines visible in the photographs : 



In addition to the lines in the above table, six of the photographs, 

 including that of August 26, give indications of the presence of a line 

 in the extreme ultra-violet. Its wave-length could not be obtained 



L 2 



