340 NINETEENTH CENTURY. pr. ill 



remains the same, and this is one out of many proofs that 

 force cannot be destroyed, but is only lost in one form to re- 

 appear in another. 



Other Experiments on Heat. — Although the experiments 

 and calculations which have proved heat to be a kind of 

 motion are some of the most interesting which have been 

 made of late years, yet they are by no means the only ones. 

 In 1811 Sir John Leslie carried on a most interesting series 

 of observations on the reflection of heat ; and the Italian 

 physicist Melloni has traced the whole passage of heat- 

 rays through different solid bodies. All these discoveries 

 are clearly and simply described in Professor Tyndall's 

 work on * Heat,' where you may also find the great addi- 

 tions that he has himself made to the work of these men. 



We must content ourselves here with remembering that 

 the physicists of the nineteenth century have shown that 

 heat is *a mode of motion,' and have traced it through 

 all its many wanderings both in earth, air, and sky. They 

 have even followed it from the sun down to our earth, 

 through the plant-world into the beds of coal which are 

 stored up in our rocks, and back again, when this coal is 

 burnt, to the motion which carries our steam-engines and 

 steam-ships across the world. All this lies before you to 

 study in books of science, but now we must pass on to 

 new discoveries in two remarkable sciences, namely, elec- 

 tricity and magnetism, which, we shall find, are closely 

 bound up with heat and motion. 



Chief Works consulted. — Rumford's 'Essays,' vol. ii. — 'Friction a 

 Source of Heat,' 1798; Davy's 'Works,' vol. ii. — 'Essay on Heat 

 and Light ; ' Joule's * Mechanical Equivalent of Heat ' — * Phil, Trans,,' 

 1850 ; Mayer's 'Forces of Inorganic Nature' — 'Phil. Mag,,* 1843; 

 Tyndall's 'Heat a Mode of Motion;' Watts's 'Diet, of Chemistry/ 

 art. 'Heat ;' Clerk -Maxwell's ' Theory of Heat.' 



