Producible by Contact and Attrition of Metals. 33 



Were the heat produced by attrition, the cause of the resulting deflections, 

 we should expect that when deflection had taken place in consequence of the 

 contact of two metals at unequal temperatures, friction, by aflbrding a new 

 source of heat, should increase the deflection in the same direction. But the 

 contrary result is obtained in a number of instances, for tlie needle passes off 

 in an opposite direction. 



If any additional proof were required on this subject, it may be found in 

 the list of metallic associations, constituting the third Table above mentioned. 

 These associations seem to prove that the deflections are not produced by the 

 heat of attrition determined to or from any particular metal of the pair ; for no 

 matter which metal is heated by external means, the needle will be deflected 

 m the same direction when attrition or contact is brought into operation. 



In fine, without some violent and gratuitous assumption, it does not seem 

 practicable to sustain the opinion that heat is the agent of attrition in produc- 

 ing these deflections. The foregoing considerations appear to me to render it 

 more probable that they are the result of a peculiar attribute of metals which 

 acts independently of heat, although it is occasionally much modified by that 



agent 



What the ultimate efiect of tribothermo-electric phenomena may be on the 

 present theory of voltaic electricity is not easy to foresee ; ingenious arguments 

 will, perhaps, be contrived to show their compatibility. Hitherto the prevail- 

 ing opinion, at least in the British Isles, has been that voltaic electricity can 

 only be evolved by chemical agency ; but in tribothermo-electric phenomena 

 the agent, whatever it may be, is developed without any chemical action ; can 

 It then be the same as that which is efiicient in voltaic phenomena ? 



In the foregoing essay it would have been my wish to have reduced the 

 number of the Laws by expressing them more generally, or to have comprised 

 them, if possible, under one comprehensive Law ; but as they are inductions 

 from facts more or less numerous, and sufficiently distinct, I soon discovered 

 my inability to express them in a more abstract form without omitting impor- 

 tant distinguishing particulars, or rendering their enunciation inconveniently 

 complex and intricate. 



The laws of thermo-electricity have been unavoidably mixed up with those 

 of tribo-electricity, a consequence of the inseparable nature of the phenomena. 



VOL. XXIII. J. 



