A HISTORY OF SCIENCE 



By the friction of two metallic plates continued for a 

 very long time, we ca^n gradually cause the cessation 

 of an immense 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 can- 

 not be regarded as = o any more than contrary mo- 

 tions can come out of nothing, or a weight can raise 

 itself. 



"Without the recognition of a causal relation be- 

 tween 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 de- 

 rived 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 vacua; but 

 let any one try to convert ice into water by pressure, 

 however enormous. The author has found that water 

 undergoes a rise of temperature when shaken violently. 

 The water so heated (from twelve to thirteen degrees 

 centigrade) 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 apparatus as often as we please ? 

 The vibratory hypothesis of heat is an approach tow- 

 ards the doctrine of heat being the effect of motion, 

 but it does not favor the admission of this causal rela- 

 tion in its full generality. It rather lays the chief 

 stress on restless oscillations. 



" If it be considered as now established that in many 



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