76 FRAGMENTS OF SCIENCE 



we are entirely dependent on atoms and molecules of 

 the latter kind. Their attractions can produce motion, 

 because sufficient distance intervenes between the attract- 

 ing atoms, and it is this atomic motion that we utilize in 

 our machines. Thus we can get power out of oxygen 

 and hydrogen by the act of their union; but once they 

 are combined, and once the vibratory motion consequent 

 on their combination has been expended, no further 

 power can be got out of their mutual attraction. As 

 dynamic agents they are dead. The materials of the 

 earth's crust consist for the most part of substances 

 whose atoms have already closed in chemical union 

 whose mutual attractions are satisfied. Granite, for in- 

 stance, is a widely diffused substance; but granite con- 

 sists, in great part, of silicon, oxygen, potassium, cal- 

 cium, and aluminium, whose atoms united long ago, 

 and are therefore dead. Limestone is composed of car- 

 bon, oxygen, and a metal called calcium, the atoms of 

 which have already closed in chemical union, and are 

 therefore finally at rest. In this way we might go over 

 nearly the whole of the materials of the earth's crust, 

 and satisfy ourselves that though they were sources of 

 power in ages past, and long before any creature ap- 

 peared on the earth capable of turning their power to 

 account, they are sources of power no longer. And here 

 we might halt for a moment to remark on that tendency, 

 so prevalent in the world, to regard everything as made 

 for human use. Those who entertain this notion, hold, 

 I think, an overweening opinion of their own impor- 

 tance in the system of nature. Flowers bloomed before 

 men saw them, and the quantity of power wasted before 

 man could utilize it is all but infinite compared with 



