THE FINITE UNIVERSE 



and not of the molecule as a whole. For example, 

 when hydrogen and oxygen are exploded, to form 

 water, the molecules of the two gases are supposed 

 to be broken up in order that by their recombina- 

 tion they may form a water-molecule. The heat 

 produced by this reaction is intense, so much so as 

 to give the impression that the attraction between 

 molecules is very small compared with the attrac- 

 tion between the atoms. This attractive force is 

 no doubt finite and measurable; it is quite prob- 

 ably due to the electrical charges the atoms are 

 known to carry. If there is an upper limit of heat, 

 it would be the extreme amount of motion these 

 electrical attractions are able to generate. It 

 is worthy of note that ordinary aluminum, when 

 ignited, seems to produce about the same tem- 

 perature as the electric arc. These two sources 

 supply us with the most intense heat we know. 

 The heat of the sun, and even of the hotter suns, 

 like Sirius, may not be greatly beyond this. The 

 subject is still obscure, and until some inventive 

 genius devises more delicate mechanical appliances, 

 we must be content with our ignorance. 



To the divisibility of matter the mind sets no 

 limits ; but nature does, at least so far as our knowl- 

 edge goes. In fancy we can think of nothing so 

 minute that we cannot conceive half of it ; but half 



8 Q 



