18 Mr. Donovan on Galvanometric Deflections 



6. When the antimony is cold and the bismuth hot, contact or attrition 

 will cause western deflection. 



From this statement it is plain that if the foregoing six conditions were laid 

 down for all the associated pairs, that one marked 2 would in each case permit 

 the needle to pass from east to west by continued attrition ; and that one 

 marked 6 would allow it to change from west to east by the same treatment. 

 In all these instances the reversal would, as already explained, be simulated; 

 that is, it would happen merely in consequence of the cooling of the metal to 

 so low a degree as to remove it from the operation of the law under which that 

 deflection had been produced : it would be a passive not an active reversal 

 (Law VI. ) ; and would not arise from any direct opposition of properties between 

 contact and attrition. 



It is obvious that the foregoing paradigm can only apply to the associated 

 pairs of metals when in each case they are placed relatively to each other as in 

 the list. The six conditions apply, for instance, to bismuth and antimony, but 

 not to antimony and bismuth : were the order antimony and bismuth, and so in 

 the rest, the conditions of simulated reversal would be those marked 3 and 5, in- 

 stead of 2 and 6. But other associations may be formed which comport them- 

 selves differently from those in the preceding list: in order to make them agree 

 with conditions 2 and 6, they must be arranged at the ends of the coil in the order 

 given in the following examples, and the temperatures must be reversed. 



Lead with antimony. 

 Tin with antimony. 

 Tin with iron. 

 Silver with antimony. 

 German silver with antimony. 

 Platinum with antimony. 



Copper with antimony. 

 Copper with iron. 

 Brass with antimony. 

 Arsenic with antimony. 

 German silver with arsenic. 

 Copper with cadmium. 



1. When the first-named metal of each associated pair is on the zinc side, 

 and both are at the same temperature, attrition gives western deflection. 



2. If the first-named metal, being on the zinc side, be cold, the other hot, 

 the deflection by contact or attrition is east. 



3. If the first-named metal on the zinc side be hot, the other cold, contact 

 or attrition gives west deflection. 



