Oxygen. 187 



the chemical power of light and heat and the electric 

 flash, and thus they are ready in every place, at every 

 moment, to renew the face of the earth. 



The affinity they have for each other is so nicely 

 balanced that under the action of living beings they 

 are decomposed and recombined to form organic 

 compounds ; and when these compounds have per- 

 formed their allotted work, they are decomposed 

 into other compounds of gaseous form, to float 

 away, until again imprisoned by the roots or spread- 

 ing leaves of the forest, or the tender herbage of 

 the meadow ; and then again they return in cease- 

 iicuit to the inorganic, air-like s: 

 h of these elements is worthy of careful study, 

 for its relation to the other three, and for the part it 

 plays in the economy of nature. 



Oxygen is the most abundant element on the 

 globe, and has the widot range of affinity. Nearly, 

 if not quite, one-half of all the solid crust of the 

 ih is composed of this gas, in combination with 

 metallic and metalloid substances. And here we 

 are struck with the numberless series of compounds 

 which oxygen gives, without which the earth would 

 be entirely unfitted, in its mineral constitution, for 

 the support of vegetable, and consequently of ani- 

 mal life. The deepest rocks which the convulsions 

 of the earth have thrown up from its very frame- 

 work, are made up chiefly of the oxides of metals 

 and silicon. And every sandstone, slatestone, and 

 limestone that makes up the sedimentary rocks, is 

 simply a combination of this gas with other elements. 



