338 BLACK. 



perature of ice until it is disturbed, when it gives out 

 heat and freezes at once, appears also to have attracted 

 his careful consideration. He contrived a set of simple 

 but decisive experiments to investigate the cause of 

 these appearances, and was led to the discovery of 

 latent heat, or the absorption of heat upon bodies 

 passing from the solid to the fluid state, and from 

 the fluid to the aeriform, the heat having no effect on 

 surrounding bodies, and being therefore insensible to 

 the hand or to the thermometer, and only by its 

 absorption maintaining the body in the state which it 

 has assumed, and which it retains until, the absorbed 

 heat being given out, and becoming again sensible, the 

 state of the body is changed back again from fluid 

 to solid, from aeriform to fluid. He never published 

 any account of this discovery, but he explained it fully 

 in his Lectures, both at Glasgow and Edinburgh, 

 and he referred to it in the paper already mentioned, 

 which was printed in the ' Philosophical Transactions ' 

 for 1775. Well, then, may we marvel that no mention 

 whatever of latent heat is made in the celebrated ' Ency- 

 clop6die,' which owed its chemical contributions to no 

 less a writer and experimentalist than Morveau. 

 The doctrine of latent heat, however, was immediately 

 applied by all philosophers to the production of the 

 different airs which were successively discovered. They 

 were found to owe their permanently elastic state to 

 the heat absorbed in their production from solid or 

 fluid substances, and to regain their fluid or solid state 

 by combining either together or with those sub- 

 stances, and in the act of union giving out in a 

 sensible form the heat which, while absorbed and 



