92 EVOLUTION THE RESULT OF CHEMICAL FORCES. 



very similar. But if the oxide of silicon, instead of being the 

 most solid substance in nature, that is quartz, had been like the 

 oxide of carbon, a permanent gas at all terrestrial temperatures, 

 the earth could never have been a solid globe. Calcium and 

 sodium are two entirely similar elemental substances. But the 

 compounds of lime are durable insoluble rock strata, while those 

 of soda are salts and alkalies. If calcium had behaved in any 

 manner like its compeer, sodium, the earth would have been 

 covered with desolate seas of caustic solutions. If nitrogen had 



O 



not been an exception to all the other elements in its inert and 

 neutral character, if it had united with oxygen as readily as any 

 one of all the others, the world would have had only seas of 

 nitric acid and an atmosphere of the fumes of ammoniacal salts. 

 Thus we might go on enumerating a thousand other contingen- 

 cies, one as probable as another, in the happening of any one of 

 which, our world, so far as we can judge, could not have existed 

 in a condition suitable to living beings. 



Ages on ages before ever there was a drop of water formed or 

 a vapor cloud had floated in space, two gases existed which had 

 the property or potency, under certain contingencies which up to 

 that time had never happened, of combining together and form- 

 ing the substance we call water. They were two out of sixty- 

 five elemental gases. They had no resemblance to, and no prop- 

 erty in common with, the vapor of water, except the gaseous 

 state. They existed in such quantity relatively to the rest, that 

 when the time came for them to combine, water should be one 

 of the most abundant materials that were to result from the 

 various chemical combinations. IsTow so far as human knowledge 

 and experiment can determine, there were thousands of possible 

 contingencies against the production of this substance which 

 apparently alone makes this world or any world inhabitable. 

 The union of oxygen with hydrogen, instead of being the most 

 inert and neutral substance in nature, might just as well 

 have been like that of oxygen with sulphur or phosphorus or 

 nitrogen, or like that of hydrogen with chlorine or iodine or 

 bromine, powerful and destructive acids: It might just as well 

 have been like the compound of oxygen and carbon, a permanent 



