AtmospJicrc. 189 



on all the elements which it has since held in its 

 unyielding grasp, the oxygen of the air was undoubt- 

 edly left as a residual substance. For, notwithstand- 

 ing the strong affinity of oxygen for other elements, 

 the amount of each element which it can hold in 

 combination is unalterably determined. When 

 every metal and metalloid that forms the crust of the 

 earth had received its portion, the oxygen of the 

 atmosphere was so much of one material in 

 in the world-making experiment. 



Nor do id this as in any sense a mere 



lucky accident. Certain it is that the whole range 

 of life upon the lepenfis upon the fact. \Ve 



ird this excess as one of the predetermined con- 

 ditions of the experiment which was tried to pre- 

 e an abode for sensitive life, and which was, 

 therefore, tried in such a manner as to secure the 

 end in view ; fr the free <>\\L;vn of the atmosphere 

 is as essential to life as the rocks, and soils, and 

 Water thai form the earth's crust. The result is the 

 same as every chemist sometimes aims at in his 

 work in the laboratory. He pours in one element or 

 compound in excess. The great Architect of the 

 universe who ordained the chemical power of oxy- 

 gen, ordained also the quantity of materials upon 

 which it should act to form the rocks and oceans ; 

 and when the eternal balance was poised, to deter- 

 mine the proportions, provision was made for the 

 atmosphere. Oxygen was not only the great pre- 

 parer of the globe for living beings, but it plays such 

 an essential part in sustaining life, that the early 



