On the Quantity of Oxygen in the Atmosphere, 565 



underlying portions of the earth, which we do not know 

 a priori. Accordingly to determine which of the opposite 

 effects has been the real one, we must have recourse to 

 geological evidence. And what geology teaches us is : — (1) 

 That the effect produced by denudation, whether it has been 

 to raise the surface or to depress it, has been accumulating — 

 all in one direction — for the immense geological age which 

 has elapsed since the existing river-systems of the earth were 

 established. And (2) that this accumulated movement 

 whether it has been an upward movement or a downward 

 has affected different parts of the continents upon the earth in 

 different degrees : it has been exerted most efficiently upon 

 those parts which we find to be now the highest ; it has 

 operated most feebly upon those which now lie the lowest ; 

 and it has affected in various degrees the other parts that 

 stand at intermediate elevations— but always in degrees pro- 

 portioned to the elevations at which we now find them. 



17. From this geological evidence (especially when ex- 

 tended to the geology of the ocean, and pursued into details), 

 we seem to me to be justified in drawing the inference that it 

 is more likely — much more likely — that of the two physically 

 possible effects of denudation, the raising or the lowering of 

 the surface, the former is that which has actually been pro- 

 duced on the earth by this agent, and that the elevations have 

 reached their present magnitude with the help of, not in 

 opposition to, denudation. And the conclusion to which the 

 geological evidence points so emphatically, is supported by 

 our finding that it leads to values for the compressibility of 

 the earth and for its plasticity which fall well within the limits 

 of physical probability. 



LIII. The Quantity of Oxygen in the Atmosphere, compared 



ivith that in the Earth's Crust. By Gerald Stoney, 



B.A.,B.K, A.M.l.C.E* 

 rt 'HE atmosphere consists of about 22*7 per cent, oxygen, 

 J_ 76 per cent, of nitrogen and argon, and I'd per cent, of 

 aqueous vapour and minor constituents ; and since its mean 

 pressure is about 1033 grammes per square centimetre, it 

 follows that there are 234*5 grammes of oxygen over every 

 sq. centim. of the earth's surface. 



Water contains eight parts of oxygen to one of hydrogen, 

 and therefore 264 grammes of water contain 234' 5 gr. of 

 oxygen. 



From this it follows that a stratum of water which is 

 * Communicated by Dr. G. Johnstone Stoney, F.R.S. 

 Phil. Mag. S. 5. Vol. 47. No. 289. June 1899. 2 Q 



