370 M. Becquerel on the Disengagement of 



that many savages, with an address and dexterity which we 

 do not possess, succeed in lighting pieces of wood by rubbing 

 them against each other with astonishing rapidity. Every thing 

 leads to the conclusion that the eflfect thus produced is owing 

 to the vibratory motion produced by the rubbing, upon the 

 atoms, and the following facts go to prove this supposition. 



When an alloy of one part of iron and two parts of antimony 

 is subjected to the action of a file, bright sparks are immediate- 

 ly produced, which proves that the temperature is raised above 

 incandescence. The percussion of flint and steel produces a si- 

 milar effect. M. de Rumford in boring a cannon placed verti- 

 cally, found so much heat produced, that he thereby boiled water, 

 in a small cavity which was favourably situated. This, then, 

 is nearly all that we know concerning the disengagement of ca- 

 loric through the agency of friction ; and thus it would appear 

 that we are completely ignorant of the part which each of the 

 bodies plays in the production of the phenomenon, both as it 

 respects its inherent nature, and the state of its surface. 



That we may determine how far each body is concerned, we 

 must endeavour to separate all the causes which obscure the 

 effect we are investigating, although, unfortunately, it is scarce- 

 ly possible to carry this purpose into execution. In fact, when 

 we rub two bodies against each other, more or less rapidly, their 

 contact being continuous, there is an evident transmission of 

 heat from the one body to the other. The quantity which is 

 transmitted from each of them, depends upon the conducting 

 power of the body, also upon its capacity for caloric, and upon 

 the state of its surface. Moreover, the caloric disengaged from 

 one of the bodies cannot be immediately ascertained before its 

 transmission into the other, with the common thermometers, be- 

 cause their indications are not instantaneous. But, notwith- 

 standing all this, means may be devised by which we may suc- 

 ceed in operating in circumstances which will overcome many 

 of the difficulties at which we have hinted, and the following 

 facts are some of the results of these arrangements. 



The apparatus with which these effects were observed, con^ 

 sists of a thermo-electrical pile, having an excellent multiplica- 

 tor. Such is its sensitiveness, that the differences of about a 

 hundredth part of a degree, of the Centigrade thermometer, be- 



