126 Sioux City Academy of Science and Letters. 



hj the eye alone, hence a more permanent means of 

 recording it was sought, and this was secured by photo- 

 graphic means at the eclipse of August, 1896, and also 

 in each succeeding obscuration of the sun to the present 

 time. The result of an investigation of all the observa- 

 tions to the present seems to indicate that the shell of 

 various metallic vapors resting upon the photosphere is 

 a true reversing layer about 600 miles thick, and is the 

 location of the dark absorption lines by means of which 

 we are enabled to unravel the secrets of the solar consti- 

 tution. This layer is cooler than the photosphere, which 

 has a temperature of about 6590 degrees centigrade, 

 according to W. E, Wilson's researches in 1901.^^^ 



Perhaps the most interesting of the solar constitu- 

 ents are the gases Helium and Coronium, both of which 

 were supposed to be solely solar products, being only 

 visible at times of eclipses, and in the prominences and 

 chromosphere by means of the spectroscope daily. 



Helium manifests its presence by a bright yellow 

 line near the sodium D lines, and the designation D3 was 

 given to it at the eclipse of 1868. It is not visible in the 

 Fraunhofer spectrum, and although it appears to be an 

 abundant element in the solar atmospheres, no trace of 

 it can be detected in the reversing layer. In 1895 Sir 

 Wm. Eamsey, while experimenting with Argon, suc- 

 ceeded in discovering Helium in a kind of pitch-blend 

 known as cleveite, whose spectrum showed the charac- 

 teristic yellow lines, and the mysterious substance was 

 found to be also a product of our own globe, though in 

 very limited quantities. Its chemical nature is unique; 

 it is monatomic, non-valent, and enters into no com- 

 binations; it has an extremely low refractive index and 

 is an excellent conductor of electricity. It is a conspicu- 

 ous substance in nearly all eruptive and quiescent 

 prominences. The writer has very frequently observed 

 these phenomena by means of the tele-spectroscope in 

 the D3 line, the forms of the delicate filaments and 

 cloud-like masses being nearly as distinct as through the 

 familiar hydrogen line in the red end of the spectrum. 



Of Coronium we know but little, seen only as a 

 bright green line at a time of a total eclipse of the sun; 

 it certainl^^ exists in large quantities in the solar vapors 



