1905.] 



On, the Stellar Line near X 4648. 



547 



It will be seen that the mean wave-length is in fairly good accord 

 with that of the unknown terrestrial line 4685-97. The line, how- 

 ever, in the nebular and bright-line-star spectra is broad and ill-defined, 

 and the estimated wave-lengths are probably somewhat uncertain, and 

 not to be depended on so much as those obtained from spectra in 

 which the line is sharply defined. If in seeking the mean wave- 

 length these probably less accurate wave-lengths be excluded, the 

 result is 4685 '9, which is in very close agreement with the position of 

 the terrestrial line. 



Rydberg has shown that the stellar line near 4686 associated with 

 the new series discovered by Pickering in the spectrum of Puppis 

 is probably the first line of the principal series furnished by hydrogen. 

 His calculated wave-length value for the line is 4687 '88,* which would 

 appear to be about two tenth-metres in error, as the corresponding 

 celestial line probably has, as is shown in the present note, a wave- 

 length near 4685-9. 



In the light of this evidence for the probable identity of the 

 terrestrial and stellar lines, it seems desirable to institute further 

 research on the spectrum of helium under varying electrical conditions, 

 with the object of possibly obtaining the terrestrial equivalents of the 

 so-called new hydrogen series of Puppis. 



DESCRIPTION OF PLATE. 



The plate shows a comparison of the spectrum (region 4450 to 4750) of the 

 chromosphere, the helium spectrum containing the line 4686, and that of 

 Orionis ( Alnitamian) . The identity of position of the helium lines, and 

 4686, with lines in the chromospheric and stellar spectra is clearly shown. 

 The fainter lines in the helium spectrum are all due to oxygen. 



' A st. Phys. Jour.,' vol. 6, p. 237. 



