64 THE YEAH. 



growth, of every thing material depends. Upon the 

 abstract nature of heat, it is but a waste of time to 

 speculate; as it would be in vain to hope to discover 

 by weight or solidity, or any other of the tangible 

 attributes of matter, that of which the uniform effect is 

 to destroy those attributes. We have no reason to 

 suppose that there is any one substance in nature 

 which the application of a sufficient heat would not 

 convert into a vapour, or aerial fluid so rare that no 

 test which could be applied would be delicate enough 

 for detecting its presence ; and therefore we need not 

 wonder that a substance (for either heat is a substance 

 or it is nothing) which can separate a dense body like 

 gold into particles so small and distant from each 

 other that we cannot weigh or even detect them, 

 should be without the range of our very nicest instru- 

 ments. In the history and philosophy of nature, we 

 have to do only with phenomena or results ; and 

 therefore it matters not whether heat be a separate 

 substance, or merely a motion, or a repulsion among 

 the atoms of bodies, by which when they are excited, 

 their cohesion or their gravitation is destroyed. We 

 know from experience that it is something that can be 

 communicated and again taken away. The absence of 

 heat, for instance, converts water into ice, from a per- 

 fectly limpid fluidity to nearly the texture of glass, 

 from that which diffused itself uniformly over the sur- 

 face of the sea, to that which can rear itself into a 

 pyramid, hundreds of fathoms or feet above the surface. 

 We know, also, that if this icy pyramid be exposed for 

 a sufficient length of time to warin air, it will be con- 

 verted into liquid water, while the air will be cooled 



