88 THE ADDRESSES, LECTURES, ETC., OF 



company being formed, statements to this effect could be seen in 

 some of our leading papers. Nothing, however, could be more 

 fallacious. When hydrogen burns, doubtless a great development 

 of heat ensues, but water is already the result of this combustion 

 (which took place upon our globe before the ocean was formed), 

 and the separation of these two substances would take precisely 

 the same amount of heat as was originally produced in their com- 

 bustion. It will thus be seen that both the solid and fluid con- 

 stituents of our earth, with the exception of coal, of naphtha 

 (which is a mere modification of coal), and the precious metals, 

 are products of combustion, and therefore the very reverse of fuel. 

 Our earth may indeed be looked upon as " a ball of cinder, rolling 

 unceasingly through space" but happily in company with another 

 celestial body the sun, whose glorious beams are the physical 

 cause of everything that moves and lives, or that has the power 

 within itself of imparting life, or motion on our earth. This 

 invigorating influence is made perceptible to our senses in the 

 form of heat, but it is fair to ask, what is heat, that it should be 

 capable of coming to us from the sun, and of being treasured up 

 in our fuel deposits both below and on the surface of the earth ? 



Definition of Heat. If this inquiry had been put to me thirty 

 years ago, I should have been much perplexed. By reference to 

 books on Physical Science, I should have learnt that heat was a 

 subtle fluid, which somehow or other, had taken up its residence 

 in the fuel, and which, upon the ignition of the latter, was sallying 

 forth either to vanish or to abide elsewhere ; but I should not 

 have been able to associate the two ideas of combustion and 

 development of heat by any intelligible principle in nature, or to 

 suggest any process by which it could have been derived from the 

 sun and petrified, or, as the empty phrase ran, rendered latent in 

 the fuel. 



It is by the labours of Mayer, Joule, and other modern physicists, 

 that we are enabled to give to heat its true significance. 



Heat, according to the "dynamical theory," is neither more 

 nor less than motion amongst the particles of the substance 

 heated, which motion, when once produced, may be changed in 

 its direction and its nature, and thus be converted into mechani- 

 cal effect, expressible in foot pounds, or horse power. By intensi- 

 fying this motion among the particles, it is made evident to our 



