6 



others in their neighbourhood, and that some of the copper lines 

 are not noticeable, proves that even before descending sufficiently 

 far to have passed through a stratum of these gases we have 

 already arrived at a sensibly higher temperature. This tempera- 

 ture in the case of some of the lines of copper and zinc appears to 

 approach, if it does not pass beyond, the temperat\ire of the 

 luminous clouds. 



The slight fluctuation of intensity in the iron lines, is conclusive 

 evidence that iron is very abundant in the solar atmosphere, and 

 ■with the exception of hydrogen is by far the largest constituent. 



There is evidence in favour of the presence of compound bodies 

 in the sun, but their density will in most cases be too high to 

 permit them, however volatile, to reach the cool parts of the sun's 

 atmosphere so as to reveal themselves in conspicuous solar lines.* 



Now if we go back to the earth, and apply what we have just 

 learned from the sun, it will be seen how easily everything falls 

 into its proper place and admits of explanation. 



We must of necessity have at the extreme limit of the earth's 

 atmosphere at this time, hydrogen, which is as abundant with us 

 as in the sun, next nitrogen and oxygen, each soaring to nearly 

 equal heights, then the vapours of such light metals as sodium and 

 potassium, then chlorine, calcium and iron, and lastly the vapours 

 of the denser and more refractory metals. 



As the earth began to cool and solidify, these last would of course 

 be the first to be condensed, and the lighter ones left are precisely 

 those that we shall find in the crust, and which make up our rock 

 masses such as granites, limestones, sandstones, &c. 



On the earth still further cooling and combination generally 

 taking place, we should have, to mention only the more important 

 reactions, the hydrogen uniting with the oxygen to form water, 

 the vapour of which would reach to the extreme limit of the 

 atmosphere, and the chlorine combining with the sodium to form 



* Those who are interested in this, the astronomical branch of the 

 subject, are referred for corroborative details to Professor Miller's lecture 

 given some months after the date of this paper before the British Association, 

 at Exeter. 



