Antecedents of Motion > Heat, and Light. 91 



servoir of water, has potential energy. If the stone be let 

 fall, its potential energy is converted into actual energy 

 during its descent, exists entirely as the actual energy of its 

 own motion at the instant before it strikes, and is transformed 

 into heat at the moment of coming to rest on the ground. If 

 the water flow down by a gradual natural channel, its poten- 

 tial energy is gradually converted into heat by fluid friction, 

 according to an admirable discovery made by Mr Joule, of 

 Manchester, about twelve years ago, which has led to the 

 greatest reform that physical science has experienced since 

 the days of Newton. From that discovery it may be con- 

 cluded with certainty, that heat is not matter, but some kind 

 of motion among the particles of matter ; a conclusion esta- 

 blished, it is true, by Sir Humphrey Davy and Count Rum- 

 ford, at the end of last century, but ignored by even the high- 

 est scientific men during a period of more than forty years. 

 Mr Joule, by a series of well-planned and executed experi- 

 ments, ascertained that a pound of water would have its 

 temperature increased by 1° (Fahrenheit), if it kept all the 

 heat that would be generated by its descent in the way de- 

 scribed above through 772 feet ; that is, the " actual " or 

 " dynamical " energy of as much heat as raises by one de- 

 gree the temperature of a pound of water, is an exact equi- 

 valent for the potential energy of a pound of matter 772 

 feet above the ground. Mr Joule also fully established 

 the relations of equivalence among the energies of chemical 

 affinity, of heat of combination or of combustion, of electrical 

 currents in the galvanic battery, of electrical currents in mag- 

 neto-electric machines, of engines worked by galvanism, and 

 of all the varied and interchangeable manifestations of calorific 

 action and mechanical force which accompany them. These 

 researches, with the theory of animal heat and motion in re- 

 lation to the heat of combustion of the food, and the theory 

 of the phenomena presented by shooting stars, due to the same 

 penetrating investigator, have afforded to the author of the pre- 

 sent communication the chief groundwork for his speculations. 

 The heat emitted by animals, and the mechanical effects 

 which they produce, are transformations of the energy of che- 

 mical affinity with which the food consumed by them com- 



