530 SPECIAL METHODS OF DISCOVERY. 



with a pound of water at 79 C., produced a mixture having 

 the temperature of 3-5 C., or exactly midway betweei 

 the two. By these experiments he proved that heat be- 

 comes latent during the liquefaction of ice. By devis- 

 ing and making other suitable experiments, he further 

 proved that, during the vaporisation of boiling water, a 

 great quantity of heat becomes latent in the evolved steam. 

 Cavendish also, in the year 1765, ascertained by experi- 

 ment, how much heat was absorbed by the melting of 

 snow, and evolved by the condensation of steam. 



It was by means of a suitable experiment, that Count 

 Eumford, in 1798, found that the common notion that 

 heat was a substance, was false, and concluded that heat 

 was a species of motion. His experiment was suggested 

 whilst in a military workshop at Munich, by observing 

 that great heat was produced by boring a cannon, and by 

 studying that phenomenon. Bacon and Locke had pre- 

 viously suggested that heat was a vibration. To test this 

 idea, Eumford bored a large piece of brass, under great 

 pressure of the borer, whilst the brass was in a gallon of 

 water ; and at the end of 2^ hours, the water actually 

 boiled, and he said, ( It would be difficult to describe the 

 surprise and astonishment of the bystanders to see so large 

 a quantity of water heated, and actually made to boil 

 without any fire.' Sir H. Davy also, in 1799, by a well- 

 conceived experiment, confirmed Eumford's result; he 

 melted ice by rubbing two pieces of it together in a vacuum, 

 at a temperature below the freezing-point of water, and 

 the result was very conclusive, because the specific heat of 

 ice is only half that of water. 



In the year 1815, Sir H. Davy, by devising and 

 making experiments upon the influence of wire gauze 

 upon flame, discovered various new truths, and was enabled 

 to invent the safety-lamp, for the invention of which he 



