TWO THEORIES OF HEAT. 73 



of heat in the world was regarded as a certain quantity, which passed 

 from one body to another, and that some substances contained, or could 

 "store away," more of the material called heat than other substances. Heat 

 was the material of fire the principle of it, or materia ignis ; and by these 

 theories Heat, or Caloric, was gradually adopted as a separate material agent 

 an invisible and subtle matter producing certain phenomena when liberated. 



So the two theories concerning heat arose at the end of the last century. 

 One, as we have said, is known as the Material, the other as the Kinetic 

 theory. The latter is the theory of motion, so called from the Greek kinesis 

 (motion), or sometimes known as the Dynamic theory of heat, from dunamis 

 (force) ; or again as Thermo-dynamics. 



But any possibility of producing a new supply of heat was denied by the 

 materialists. They knew that some bodies possessed a greater capacity for 

 heat than others; but Count Rumford, at Munich, in 1797, astonished an 

 audience by making water boil without any fire ! He had observed the 

 great extent to which a cannon became heated while being bored in the 

 gun factory, and influenced by those who maintained the material theory 

 of heat, paid great attention to the evolution of heat. He accordingly 

 endeavoured to produce heat by friction, and by means of horse power he 

 caused a steel borer to work upon a cylinder of metal. The shavings 

 were permitted to drop into a pan of water at 60 Fahrenheit. In an hour 

 after the commencement of the operation the temperature of the water 

 had risen to 107: in another half-hour the heat of it was up to 142: 

 and in two hours had measured 170. Upon this he says: "It is hardly 

 necessary to add that anything which any insulated body or system of 

 bodies can continue to furnish without limitation cannot possibly be a 

 material substance, and it appears to me to be extremely difficult, if not 

 quite impossible, to form any distinct idea of anything capable of being- 

 excited and communicated in these experiments except by motion" 



A few years later Sir Humphrey Davy made his conclusive experi- 

 ments, and the Material theory of heat received its death-blow. 



Sir Humphrey Davy referring to the fact that water at a freezing 

 temperature has " more heat in it " (as it was believed) than ice at the same 

 temperature said : " If I, by friction, liquify ice, a substance will be 

 produced which contains a far greater absolute amount of heat than ice. 

 In this case it cannot reasonably be affirmed that I merely render sensible 

 heat which had been previously insensible in the frozen mass. Liquification 

 will conclusively prove the generation of heat. 



This reasoning could not be doubted. Sir Humphrey Davy made the 

 experiment. He rubbed together two pieces of ice in the air, and in 

 a vacuum surrounded by a freezing mixture. The ice became liquified, 

 and so the generation of heat by " mechanical means " was proved. Its 

 immateriality was demonstrated, but the Material theory was not even then 

 abandoned by its adherents. 



So things continued, until in 1842-3, Doctor Julius Meyer, of Heilbronn,. 



