4 Mr. Henry Wilde on Helium and 



The doubleness of the yellow line of the cleveite gas 

 led directly to a closer observation of the chromospheric 

 line by Huggins,* Lockyer, and Professor Hale of Chicago, t 

 Each of these observers has found that the solar helium 

 line is also double. Mr. T. Thorp, of Whitefield, the 

 inventor of several valuable spectroscopic appliances to 

 the telescope, has also, by means of a Rowland grating of 

 14,438 lines to the inch, and a fourth-order spectrum, 

 divided D 3 . Through the kindness of Mr. Thorp, I have 

 been able to confirm the observations which have, up to 

 the present time, been made on the doubleness of the 

 yellow line of solar helium. 



Not only is the doubleness of the chromospheric line 

 established, but its components are of unequal width, and 

 the weaker line is on the less refrangible side of the 

 spectrum, as in the gas from cleveite. Professor Hale has 

 determined the difference in the wave-lengths of the 

 components of D 3 to be 0*357. Moreover, Lockyer has 

 observed that five other prominent lines of the new gas 

 coincide with the chromospheric lines 7066, 6678, 5016, 

 4922, and 44724 The only question now open for dis- 

 cussion as to the identity of solar and terrestrial helium 

 is the difference in the wave-lengths of the double line 

 as determined by the several observers. Crookes, as we 

 have seen, pronounced the yellow line of terrestrial helium 

 to be single. Ramsay subsequently observed the line 

 double, and estimated the distance between them to be 

 ■£s part of that between the sodium lines§ = 0*120 tenth 

 metres. Runge and Paschen observed a difference of 

 0*323 between the components of the yellow line, while 

 Professor Hale, as I have said, makes the difference 

 between the same components of solar helium 0*357. 



* Chemical News, July 19, p. 27. t Nature, August 1, p. 327. 



\Proc. Roy. Soc., June 13, 1895. 



§ Paper read before the Chem. Soc, June 20, 1895. 



