12 TRANSACTIONS AND PROCEEDINGS OF THE [Sess. i.xi. 



constantly accumulating. "We have only to look at the rocks 

 of which the earth's crust is composed to be assured that at 

 one time this planet was a molten ball on which there was 

 no organic matter, and now it is clad in a dress of living 

 green, and teeming everywhere with life. That vegetable 

 and animal life should have increased so abundantly, 

 requires that either there must at one time have been an 

 immense store of ammonia in the atmosphere, which has 

 gone on constantly diminishing, or there must have been, 

 and there must be now, some process going on on a large 

 scale whereby ammonia is being formed out of the free 

 nitrogen of the air. 



We have no reason to suppose, however, that there ever 

 was a larger store of ammonia in the air than there is at 

 present. The certainty is rather that at one time, viz., when 

 the earth was at a white heat, there was no ammonia in our 

 atmosphere at all. A red heat suffices to decompose it 

 into its two component gases, nitrogen and hydrogen — one 

 volume of the former and three of the latter, — and these on 

 cooling do not again unite. It is hard to see how ammonia, 

 if it did exist in the atmosphere at that time, could escape 

 decomposition, and the fact that in the atmosphere there 

 is scarcely a trace of hydrogen, and, moreover, that what 

 little there is can be easily accounted for by volcanic action, 

 we naturally come to the conclusion that there was no 

 ammonia in the original atmosphere of the earth. We 

 have therefore good reason to believe that the total amount 

 of ammonia in the atmosphere is now not less, but probably 

 more than it ever has been. 



Seeing that there are so many ways in which combined 

 nitrogen may be set free, and that the quantity of com- 

 bined nitrogen on tlui gloljc is on the increase, there must 

 be some process of a widespread general kind going on 

 around us whereby the free nitrogen of the air is being 

 brought into combination. 



Despite the dictum of weighty chemical authorities 

 that plants could not convert free into combined nitrogen, 

 there remained many who l)elieved that they must possess 

 that power; for if it were not possessed by plants, there 

 seemed to be no other dii'ection in wliich to account for the 

 ordinary conditions of organic, life; on the globe. 



