14^ THERMODYNAMICS OF SOLIDS. 



theoretical anticipation of results not previously observed 

 to exist, or only incidentally observed ; as in the case of 

 india-rubber, which, when placed between the lips and 

 stretched, produces a sensation of warmth, a phenomenon 

 commented on by Mr. Gough in the Society's Memoirs, 

 Vol. I., second series. 



Sir William Thomson had deduced from the general 

 theory of thermo-dynamics, that when an elastic body has 

 its form changed by definite forces the heat which becomes 

 latent is the product of the absolute temperature multiplied 

 by the forces, multiplied again by the change of dimensions 

 in the direction in which the force acts, caused by raising 

 the temperature of the body one degree, whence, knowing 

 the specific heats, weight, and coefficient of expansion, the 

 alteration of temperature consequent on subjecting a solid 

 or liquid to stress could be quantitatively found. 



Joule verified the truth of this theory in the cases of iron, 

 hard steel, cast iron, copper, lead, gutta-percha, vulcanized 

 india-rubber, various kinds of wood, and water. 



At the conclusion of his paper " On some Thermo- 

 dynamic properties of solids," Phil. Trans, 1859, Joule, 

 referring to his last determination, in which he had measured 

 the heating and cooling effect in a spiral spring to be 

 o°'003o6 Fah., while the theoretical effects to be expected 

 were 0^00406, remarks : — 



" Thus even in the above delicate case is the formula of 

 Professor Thomson, completely verified. The mathematical 

 investigation of the thermo-elastic qualities of metals has 

 enabled my illustrious friend to predict with certainty a 

 whole class of highly interesting phenomena. To him 

 specially do we owe the important advance which has 

 recently made a new era in the history of science, when 



