1912] The Ottawa Naturalist. 31 



equally true of celestial as of terrestrial bodies, and when the 

 light of the sun or of a star is projected on the slit of a spectro- 

 scope, we have at once an unfailing and accurate criterion as 

 to the elements present in the atmosphere of the sun or star. 



When we analyse the light of the sun in this way we find 

 lines in its spectrum due to most of the terrestrial elements, and, 

 as we have good grounds for believing that earth and sun had 

 a common origin, we can safely assume that their composition 

 is identical, and that, if some terrestrial elements do not show 

 in the solar spectrum, it is either on account of their relative 

 scarcity, or because their spectrum is weak and overpowered 

 by others. On the other hand there is no convincing evidence of 

 the presence in the sun of any elements not found on the earth, 

 although this was not the case a few years ago. There is always 

 present in the spectrum of the outer atmosphere of the sun a 

 very bright yellow line of which there was no known terrestrial 

 counterpart and the hypothetical gas producing this line was 

 called helium. Sir Wm. Ramsay, in 1895, in examining the 

 spectrum of a gas, obtained by heating a rare mineral called 

 cleveite, found that it gave a strong line in exactly the same 

 position as the yellow solar line and was consequently due to 

 the same element, helium. Helium is a very light gas, does not 

 combine with any other elements, and has not sufficient mass 

 to enable the earth's attraction to retain it in the atmosphere. 

 Consequently most of the helium, except that occluded by the 

 mineral cleveite and, as we now know, that obtained from the 

 degradation of radium had dissipated into space. This is an 

 interesting incident, and as will be seen later a very important 

 and widespread one a new element discovered in the sun before 

 being found on the earth. 



Although we might possibly have reasoned from other 

 evidence of the probable identity of composition of the sun and 

 earth, we certainly could not, without the spectroscope, have 

 known anything definite of the constitution and physical con- 

 dition of the stars. When, however, we examine their spectra 

 we find nearlv fortv per cent, of them. practically identical with 

 the sun, and the remainder shading off by gradual degrees into 

 simpler and simpler spectra until only the lines due to hydrogen 

 and to hydrogen and helium remain. The disappearance of the 

 lines of the heavier elements is not, however, an indication that 

 they are not present, but only that, owing to the higher tempera- 

 ture of the hydrogen and helium stars these light elements are 

 the chief constituents of their outer atmospheres and the elements 

 of higher atomic weight are nearer the centre. 



The evidence then, spectroscopic and otherwise, of the 

 chemical unity of all the matter in the universe is indisputable. 



