516 Proceedings. 



was long ago made, as a vague generalization, that the fuel we are now using, 

 and from which we derive those vast stores of power which are now available 

 for the service of man — to pci-form the minutest labour, in weaving the finest 

 fabrics, or to drive the vast steamship across the Pacific — is produced by the 

 sunshine of ages long past, stored away in the great deposits of coal, resulting 

 from ancient vegetation ; or as George Stephenson, with a sagacity of mind in 

 advance of the science of his day, answered, when asked what was the 

 ultimate cause of motion of his locomotive engine, " that it went by the 

 bottled-up rays of the sun." But this brilliant suggestion has not merely now 

 become a truism apprehended by every one, but we can at once calculate the 

 quantity of energy so stored up, and ascertain in accurate measure the light 

 and power which lie there dormant, and which may again be brought forward 

 for the use and at the will — it may be for the destruction — of man. 



Dr. Siemens, in a remarkable lecture given on the occasion I have so often 

 refeiTed to, says : — " But you will 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 '? If this enquiry 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 is a subtle fluid, 

 which, somehow or other, had taken up its residence in the fuel, and which, 

 upon ignition of the latter, was sallying forth either to vanish or to abide else- 

 where j 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, Clausius, Kanken, and other modern jihysicists, that we are 

 enabled to give to heat its true significance. Heat, according to the dynamical 

 theory, *is neither more nor less than motion among the particles of the 

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

 direction and nature, and thus be converted into mechanical effect, expressible 

 in foot-pounds or horse-power. By intensifying this motion among the 

 particles it is made evident to our visual organ by the emanation of light, 

 which again is neither more nor less than vibratory motion imparted by the 

 ignited substance to the medium separating us from the same.' According to 

 this theory, which constitutes one of the most important advances in science 

 of the present century, heat, light, electricity, and chemical action are only 

 different manifestations of energy of matter, capable of being changed from 

 the one form of energy to another, but being as indestructible as matter itself. 

 Energy exists in two forms, 'kinetic energy,' or force, manifesting itself to 

 our senses as weight in motion, as sensible heat, or as an active electrical 

 current, and 'potential energy,' or force in a dormant coniUtion. In 



