316 Mr. J. Stevenson on the Chemical and 



on plants, and he found, by calculating the weight of fuel 

 corresponding to the total free oxygen of the atmosphere, 

 an upper limit to the amount of fuel in the world, viz. 

 340,000,000,000,000 (340 million million) tons. 



However, in his address to the Victoria Institute on the 

 Age of the Earth, his attitude on the oxygen question is 

 much less definite and decided. In § 40 of the printed 

 address he says that there is good reason for believing 

 that there was no free oxygen in our primitive atmo- 

 sphere, because the gases found in the cavities of granite and 

 basaltic rock contain nitrogen, carbonic acid, and water, but 

 no free oxygen. Further, some specimens of such rocks 

 or minerals even contain free hydrogen, and when they do 

 not contain free hydrogen they contain native iron or mag- 

 netic oxide of iron. He considers, therefore, " that we may 

 judge that probably all the oxygen of the hot nebula which 

 became the earth fell into combination with hydrogen and 

 other metallic vapours on the cooling of that nebula ; and 

 though oxygen is known to be the most abundant chemical 

 element on the earth, none of it was left out of combination 

 to give free oxygen in our primitive atmosphere." His 

 position here is obviously the same as that taken up in his 

 Toronto address, but after discussing some other points 

 connected with his general subject (the Age of the Earth), 

 though not bearing directly on the free oxygen question, he 

 goes on to say : "It seems improbable that the average of 

 the whole earth — dry land and sea-bottom — contains at 

 present coal or wood or oil or fuel of any kind, originating 

 in vegetation to so great an extent as 0*7 07 of a ton per 

 square metre of surface ; which is the amount at the rate of 

 one ton of fuel to three tons of oxygen that would be required 

 to produce the 2*3 tons of oxygen per square metre of surface 

 which our present atmosphere contains. Hence it seems 

 probable that the earth's primitive atmosphere must have 

 contained free oxygen." He adduces no other reason for 

 this supposition than the above, viz., the difficulty in believing 

 that there is so great an amount of fuel or combustible matter 

 due to vegetation existing on the earth. 



Probably most people will have the same difficulty in this 

 matter that Lord Kelvin has, but still there is ample room 

 to discuss the question further. The problem may be attacked 

 in several ways with a fair degree of confidence or hopeful- 

 ness in the obtaining of a satisfactory answer, or at least we 

 may look at it from several standpoints, and thereby gain a 

 clearer conception of its nature and scope. 



The first and most obvious standpoint or line of inquiry 



