ASTRO-PHYSICS 283 



through the gases evolved from a specimen of 

 the mineral cleveite, and by this means isolated 

 the gas helium, thus showing that the element, 

 first discovered in the sun, was present also upon 

 the earth. The complete spectrum of helium 

 contains two sets of lines, one in the yellow and 

 one in the green. In the laboratory these two 

 sets are usually found together, though, by 

 manipulating an electric discharge in helium, 

 separation may be effected. In the light of the 

 sun, too, the yellow line is sometimes found with- 

 out the green. Other separations of the same 

 kind between the constituents of the spectra of 

 certain elements have also been observed, and 

 have sometimes suggested the idea of atomic 

 dissociation. Other explanations, however, seem, 

 on the whole, more probable. Professor J. J. 

 Thomson has shown that, when an electric 

 discharge passes through rarified hydrogen, the 

 red line becomes more intense near the positive 

 and the green line near the negative electrode. 

 This observation indicated a separation of 

 hydrogen molecules into positive and negative 

 parts giving different spectra. Taken in con- 

 junction with more recent work on the enhance- 

 ment of lines by ionization, it is very suggestive 

 in relation to solar and stellar physics. 



During total eclipse, a vast radiance sur- 

 rounding the sun, known as the corona, springs 

 into view. Spectroscopic examination shows 

 that hydrogen, helium, and calcium, the main 

 constituents of the chromosphere, are absent in 

 the corona. The principal part of the light 

 seems to be due to a brilliant green line, not 

 produced by any terrestrial substance. The 



