12 THE HARMONIES OF NATURE. 



iron tools, and savage nations usually make fire by rubbing two 

 pieces of wood against each other. Percussion and compression 

 likewise produce heat. A cannon-ball, on striking a thick sheet 

 of iron with full force, will instantly raise its temperature to 

 red-heat ; and on suddenly compressing air to about one-fifth 

 of its previous volume it will set fire to cotton. Electricity, 

 chemical changes, the process of life, are also generators of 

 heat; it rises out of the craters of volcanoes, or gushes in 

 thermal springs from the bowels of the earth. 



A very general effect of heat is its expanding force. With 

 a few remarkable exceptions, it universally appears as the mighty 

 opponent of cohesion, as the adversary of terrestrial attraction. 

 First it increases the volume of solid bodies, then it reduces 

 them into a liquid state, and finally converts them into gases 

 a phenomenon which no other agent is capable of producing. 

 Hence the state of cohesion of all bodies solely depends upon 

 their temperature. Placed at a different distance from the sun, 

 our earth would offer a very different aspect : if considerably 

 nearer, enormous quantities of water would constantly be vola- 

 tilised, and then again precipitated in terrific showers ; if far 

 removed, the sea itself would be converted into a solid body, 

 and the circulation of fluids, the prime agent of vegetable 

 and animal life, be arrested. Thus our existence depends 

 upon the degree of heat resulting from the actual distance 

 of our planets from the sun ; and as we cannot possibly attri- 

 bute our origin to chance, thus also it is surely not this blind 

 capricious power, but the allwise providence of a Supreme 

 Being, which, myriads of years before the breath of life was 

 instilled into man, determined the distance of the earth from 

 the sun, that it might one day become his residence. 



If, as is by no means improbable, Mercury and Venus or 

 Jupiter and Saturn are the abodes of rational beings, these must 

 inevitably be very differently formed from us, as they dwell 

 on planets where all the conditions of organic life are so totally 

 different ; but as harmony reigns everywhere on earth, we cannot 

 doubt that, whatever their form, they will in every respect be as 

 perfectly adapted to their various abodes as we to our terrestrial 

 habitation. 



With respect to their relations to heat, we find a remarkable 

 difference in various substances or bodies. Some change their 



