M. J. R. Mayer on the Forces of Inorganic Nature. 375 



other. By the friction of two metallic plates continued for a 

 very long time, we can gradually cause the cessation of an im- 

 mense quantity of movement ; but would it ever occur to us to 

 look for even the smallest trace of the force which has disappeared 

 in the metallic dust that we could collect, and to try to regain it 

 thence ? We repeat, the motion cannot have been annihilated ; 

 and contrary, or positive and negative, motions cannot be regarded 

 as =0, any more than contrary motions can come out of nothing, 

 or a weight can raise itself. 



Without the recognition of a causal connexion between motion 

 and heat, it is just as difficult to explain the production of heat 

 as it is to give any account of the motion that disappears. The 

 heat cannot be derived from the diminution of the volume of the 

 rubbing substances. It is well known that two pieces of ice 

 may be melted by rubbing them together in vacuo ; but let any 

 one try to convert ice into water by pressure*, however enor- 

 mous. Water undergoes, as was found by the author, a rise of 

 temperature when violently shaken. The water so heated (from 

 12° to 13° C.) has a greater bulk after being shaken than it had 

 before; whence now comes this quantity of heat, which by 

 repeated shaking may be called into existence in the same appa- 

 ratus as often as we please ? The vibratory hypothesis of heat 

 is an approach towards the doctrine of heat being the effect of 

 motion, but it does not favour the admission of this causal rela- 

 tion in its full generality; it rather lays the chief stress on 

 uneasy oscillations (unbehagliche Schwingungen). 



If it be now considered as established that in many cases 

 (exceptio confirmat regulam) no other effect of motion can be 

 traced except heat, and that no other cause than motion can be 

 found for the heat that is produced, we prefer the assumption 

 that heat proceeds from motion, to the assumption of a cause 

 without effect and of an effect without a cause, — just as the 

 chemist, instead of allowing oxygen and hydrogen to disappear 

 without further investigation, and water to be produced in some 

 inexplicable manner, establishes a connexion between oxygen 

 and hydrogen on the one hand and water on the other. 



The natural connexion existing between falling force, motion, 

 and heat may be conceived of as follows. We know that heat 

 makes its appearance when the separate particles of a body 

 approach nearer to each other : condensation produces heat. 



* Since the original publication of this paper, Prof. W. Thomson has 

 shown that pressure has a sensible effect in liquefying ice (Conf. Phil. Mag. 

 S. 3. vol. xxxvii. p. 123); but the experiments of Bunsen and of Hopkins 

 have shown that the melting-points of bodies which expand on becoming 

 liquid are raised by pressure, which is all that Mayer's argument requires. — 

 G. C. F. 



