Producible by Attrition and Contact of Metals. 13 



•wooden handle, be connected with the zinc side of the galvanometer ; and a 

 hemisphere of antimony with the silver side. Both metals being at the tem- 

 perature of tlie air, their natural deflection when rubbed together would be 

 western. If the bismuth be now tliorouglily heated by being plunged in boil- 

 ing water, on withdrawing it, and bringing it in contact with the cold antimony, 

 the needle will move eastward ; and while it is thus moving, if the two metals 

 be rubbed together, the eastward motion, far from being interrupted, will con- 

 tinue until the needle reach perhaps 90". If the attrition be continued, the 

 needle will very slowly pass to zero ; and, having reached it, will move on 

 perhaps to 80° west, not very far from which it will remain while attrition is 

 continued. 



Law VI. The experiment will succeed in a very striking manner with the 

 revolving apparatus hereafter to be described. 



The circumstance that during attrition the needle passes from east to west 

 (a change which obtains equally in the case of many other associations of metals) 

 has given origin to the belief that attrition always reverses the deflection pro- 

 duced by thermo-contact, and that such reversal is a counteracting effect of the 

 influence of attrition, as such, on that of contact. It is proper to state, at full 

 length, grounds of dissent from this opinion. 



In the instance under consideration, the effect of bringing hot bismuth in 

 contact with cold antimony, as above mentioned, is to produce eastern deflection. 

 If, after the contact has continued a moment or two, the metals be moderately 

 rubbed together, the deflection, instead of being reversed, as a peculiar effect of 

 attrition, is continued in the same direction as at first ; at least this is true while 

 there is considerable inequality of temperature between the metals, and more so 

 when cadmium is substituted for antimony. But in the progress of rubbing, 

 the bismuth is reduced in temperature by imparting heat to the antimony: the 

 two metals are brought so near equality, one by parting with heat, and the 

 other by receiving it, that, in conformity with Law xiv., the natural deflection 

 begins to take place, which, when the two metals are respectively stationed at 

 the above-mentioned ends of the coil, is western : hence there is a change of 

 direction from east to west. (Law vi.) 



In accordance with this view, it will be found that the smaller and fewer 

 are the touching points of the two metals applied to each other, the greater 



