8 MATTER, LIVING FORCE AND HEAT. 



certainty, that these motions of air and water, constituting 

 living force, are not annihilated by friction. We lose sight 

 of them, indeed, for a time ; but we find them again repro- 

 duced. Were it not so, it is perfectly obvious that long ere 

 this all nature would have come to a dead standstill. 

 What, then, may we inquire, is the cause of this apparent 

 anomaly ? How comes it to pass that, though in almost all 

 natural phenomena we witness the arrest of motion and 

 the apparent destruction of living force, we find that 

 no waste or loss of living force has actually occurred ? 

 Experiment has enabled us to answer these questions 

 in a satisfactory manner ; for it has shown that, wherever 

 living force is apparently destroyed, an equivalent is pro- 

 duced which in process of time may be reconverted into 

 living force. This equivalent is heat. Experiment has 

 shown that wherever living force is apparently destroyed or 

 absorbed, heat is produced. The most frequent way in 

 which living force is thus converted into heat is by means 

 of friction. Wood rubbed against wood or against any hard 

 body, metal rubbed against metal or against any other 

 body — in short, all bodies, solid or even liquid, rubbed 

 against each other are invariably heated, sometimes even so 

 far as to become red-hot. In all these instances the 

 quantity of heat produced is invariably in proportion to the 

 exertion employed in rubbing the bodies together — that is 

 to the living force absorbed. By fifteen or twenty smart 

 and quick strokes of a hammer on the end of an iron rod of 

 about a quarter of an inch in diameter placed upon an anvil 

 an expert blacksmith will render that end of the iron visibly 

 red-hot. Here heat is produced by the absorption of the 

 living force of the descending hammer in the soft iron ; 

 which is proved to be the case from the fact that the iron 



