S7S M. Becquerel on the Disengagement of 



periments we are describing, that is to say, that the time dimi- 

 nishes in proportion as the increase augments from beyond 60*=> 

 to 92°. This result is connected with the propagation of heat 

 and electricity in bodies. 



Let us now take two bodies of the same nature, quite equal 

 in size, and arranged as already described. Let us, for example, 

 take two disks of cork, the one of which shall have its surface 

 smooth, and the other made thoroughly rough. If one of these 

 be rubbed against the other in a regular and steady manner, 

 and they are then presented simultaneously to the two faces of the 

 thermo-clectrical pile, the needle immediately traverses, and its 

 direction indicates that the roughened disk has acquired more 

 heat than the other, and this in a ratio which varies with the 

 rapidity of the friction. Precisely the same result follows when 

 a piece of polished glass is rubbed upon a portion of rough 

 glass. In the circumstances in which we have operated the 

 former has acquired only half the heat of the latter. It fol- 

 lows then, that the absorbing power of bodies exerts an in- 

 fluence upon the disengagement of caloric during friction. 

 This law, however, does not appear to be general, for white sa- 

 tin acquires more caloric than black satin, which has a greater 

 absorbing power. 



If bodies of different natures be submitted to experiment, 

 the following results are obtained. Experiment \st^ with po- 

 lished glass and cork ; — here the former substance acquires 

 more heat than the latter, in the ratio of 34 to 5. 2f?, with 

 rough glass and cork ; — here the ratio is as 40 to 7. 3^, with 

 silver and cork ; — the ratio in this case is as 50 to 12. 4^/i, 

 with caoutchouc and cork ; — the ratio here is as 29 to 11 ; and 

 so with many more. Regarding these, we observe that the nu- 

 merous results which we have obtained from the friction of dif- 

 ferent bodies, do not supply us with any simple laws, on ac- 

 count of the many different causes which all bear on the gene- 

 ral result. It appears only, that the nature of a hody^ an ab- 

 straction made, distinct from its conducting power, exercises an 

 influence which the state of the surface does not always destroy. 

 We have found it impossible hitherto to discover the cause of 

 this influence, which depends on the nature of the bodies, and 

 probably upon the arrangement of their atoms. But it is no 



