830 POPULAR SCIENCE MONTHLY. 



Another most interesting discovery is that of helium, which 

 was made by Professor Ramsay, in 1895, while examining the 

 mineral cleveite for argon, when, besides the spectrum of argon, he 

 observed another bright line not belonging to that spectrum, which 

 Mr. Crookes recognized as identical with the line D 3 which Pro- 

 fessor Lockyer had observed in 1868 in the spectrum of the solar 

 chromosphere, and which he attributed to an element not yet 

 known on the earth — helium. The same line was afterward found 

 in the spectra of other fixed stars, and the conclusion was drawn 

 that helium exists in large quantities outside of the earth. On our 

 planet it seems, however, to be very rare, and may even be ranked 

 among the rarest elements. Yet it has been almost discovered 

 several times. Palmieri observed the line of helium in his re- 

 searches on the lava of Vesuvius, but did not push the matter 

 further; and Hillebrand in 1891 obtained in the spectrum of the 

 gas formed by uranite lines which were presumptively those of 

 helium. Since its discovery, helium has been found in a consider- 

 able number of minerals, generally associated with uranium, yttrium, 

 and thorium; in mineral waters and, in extremely small quantities, 

 in atmospheric air. Next to hydrogen, it is the lightest of the gases, 

 and from this peculiarity Stoney draws an explanation of the fact 

 that these two elements exist only in very small quantities in a free 

 state on the earth, while they are diffused in enormous masses 

 through the universe. The relatively small force of the earth's 

 gravitation does not furnish an adequate counterpoise to the ve- 

 locity of their molecules, and they escape from the atmosphere of the 

 earth, unless they are restrained by chemical combination. They 

 then collect around the great centers of attraction constituted by 

 the stars, in the atmosphere of which they exist in large quan- 

 tities. 



The study of the spectrum of helium is extremely important, 

 because it gives interesting data concerning the nature of distant 

 celestial bodies. It also, as the labors of Runge and Paschen have 

 shown, suggests doubts concerning the elementary character of the 

 new substance. Whatever it may be, if we have to suppose that 

 helium is composed of two gases (Mr. Lockyer has proposed the 

 name of asterium for the second), one of the two gases probably has 

 a boiling point very near the absolute zero, and in any case below 

 — -2G4° C; for the master in liquefaction of gases, M. K. Olszewsky, 

 has not up to this time succeeded in provoking a change of state of 

 helium, and he proposes to use this gas for filling gas thermometers 

 for measuring extremely low temperatures. Helium has shown 

 itself thus far as refractory as argon to all chemical combination, 

 and so great an uncertainty reigns over the position to be attributed 



