EFFECTS OF DESTEOYED MOTION. 255 



duction of heat, and the heat some other cause than the 

 motion. 



An attempt to ascertain the effects of ceasing motion has 

 never yet been seriously made ; without, therefore, wishing to 

 exclude d priori the hypothesis which it may be possible to 

 set up, we observe only that, as a rule, this effect cannot be 

 supposed to be an alteration in the state of aggregation of the 

 moved (that is, rubbing, &c.) bodies. If we assume that a 

 certain quantity of motion v is expended in the conversion of 

 a rubbing substance m into n, we must then have m-{-v=n, 

 and n=m-\-v ; and when n is reconverted into w, v must ap 

 pear again in some form or other. By the friction of two 

 metallic plates continued for a very long time, we can grad 

 ually cause the cessation of an immense quantity of move 

 ment ; but would it ever occur to us to look for even the 

 smallest trace of the force which has disappeared in the me 

 tallic 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 =O, any more than contrary motions can come out of 

 nothing, or a weight can raise itself. 



Without the recognition of a causal connection between 

 motion and heat, it is just as difficult to explain the produc 

 tion 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 to 

 gether in vacuo ; but let any one try to convert ice into water 

 by pressure,* however enormous. Water undergoes, as was 



* 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 Bunsua 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. 



