12 Ramsay, The Newly Discovered Eleinents. 



that it was possible to classify the spectral lines of helium 

 in two distinct classes, each consisting of three series; and 

 as they had then drawn the deduction, subsequently 

 retracted when they discovered that the spectrum of 

 oxygen admitted of precisely similar analysis, that helium 

 must be a mixture of two gases, it was thought more 

 probable that the unknown gas would be found in crude 

 helium that in crude argon. Hence the experiments on 

 argon were not further followed out. 



It appeared probable, from Dr. Johnstone Stoney's 

 ingenious speculations on the " Atmospheres of Planets 

 and Satellites," that the missing gas should be a constituent 

 of the earth's atmosphere ; for its presumed density, lo, 

 would render it unlikely that it should escape from the 

 attraction of the earth, by virtue of its own proper motion. 

 It will be remembered that Dr. Stoney entertains the view 

 that while the moon, owing to its comparatively small 

 mass, is incapable of holding on its surface any gas known 

 to us, except, possibly, carbonic anhydride, the earth, owing 

 to its greater mass, is capable of holding all gases with a 

 density greater than about 7 ; while the enormously 

 greater mass of the sun accounts for the spectrum of 

 hydrogen and of helium having been seen in the light 

 which it emits. Some doubt may be entertained regarding 

 the validity of this theory, seeing that Dr. Travers and I 

 have recently verified the work of Professor Kayser, and 

 of Dr. Friedlander, each of whom, independently, saw the 

 helium lines in the spectrum of atmospheric argon ; we 

 have succeeded in isolating the helium in relatively con- 

 siderable quantity. And still more recently. Professor 

 Gautier has detected hydrogen among the constituents of the 

 earth's atmosphere, not only, as had been done previously, 

 in the atmosphere in the neighbourhood of volcanoes, but 

 in the atmosphere of P^ris. Yet, in support of Dr. Stoney's 



