Producible by Attrition and Contact of Metals. 31 



if experiment should hereafter prove the possibility of such decompositions, it 

 would prove nothing in favour of the identity liere disputed ; it is indeed only 

 what should follow from the constitution which, in my former essay, I liave 

 attributed to the electric fluid.* 



There is no observable connexion between the deflection produced by 

 chemical action on the two metals, and those caused by tlieir lliermo-contact or 

 attrition : they are frequently in opposite directions with the same metals, and 

 the degrees of deflection efiected by these several methods on the same metals 

 are very different. Thus the chemical action of spring water on bismuth and 

 antimony is so feeble that the deflection may amount to but 4", when with the 

 same galvanometer thermo-contact or attrition of these metals will cause tlie 

 needle to traverse the whole quadrant, or even the whole circle, by a sudden 

 impulse. 



Conclusion. 



Having now made such observations as seemed necessary on the Laws 

 which I conceive to regulate the motions of the magnetic needle, when under 

 the influence of the agent developed by thermo-contact and attrition of metals, 

 I proceed to consider the question whether these deflections are produced by 

 friction as a primary cause, or by the heat which friction generates. On this 

 subject a difference of opinion prevails amongst philosophers. Professor Erman, 

 the latest authority, conceived that the deflection " is a mere consequence of 

 the heat produced by the action of rubbing." 



The fact has, I trust, been sufliciently established, in the foregoing pages, 

 that there are certain metals which, when rubbed together at equal tempera- 

 tures, give a deflection of an opposite kind to that which results from contact 

 of the same metals at unequal temperatures. Now if the deflection caused by 

 rubbing the metals together at equal temperatures were not produced by fi-ic- 

 tion as a primary cause, but secondarily by the heat consequent on that friction 

 why should it take place on the side of the magnetic meridian opposite to that 

 on which it would have been had any artificial source of heat been supplied. 

 It may no doubt be argued, that as friction develops heat, this heat might be 

 unequally divided between the two metals, being absorbed more rapidly by 



* Philosophical Magazine, 1852. 



