1884.] 



Explanation of Hall's Phenomenon. 



347 



resulted in an opposite deflection of the galvanometer. The arrange- 

 ment is indicated in fig. 5, where A and B are the clamps between 

 which the wire is suspended, C the pincers, and G the galvanometer. 



The directions taken by the currents through the hot junctions are 

 given in the following table : — 



Table. 



S = stretched. U=unstretched. 



Metals. 



Form used. 



Current. 



Hall's sign. 



Wire and foil, pure 



Wire and sheet, annealed .... 



Wire, commercial 



Wire and foil 



Wire 



Wire and foil 



Foil, purity 99 "9 per cent 



Wire, commercially pxire , 



Jewellers' 18 ct. wire and sheet 



Jewellers' 15 ct., sheet 



Wire and foil 



Wire and foil, pure 



Kod, 8 millims. diameter 



Ribbon 



Foil 



Foil (assay) 



S to U 

 U to S 

 S to U 

 IT to S 

 S to IT 

 S to U 

 S to IT 

 U to S 

 S to IT 

 S to U 

 S to U 

 U to S 

 U to S 

 S to U 

 S to U 

 No current. 



(?) 



mi. 



It will be seen that in every case, excepting that of aluminium and 

 one out of five specimens of gold, there is a perfect correspondence 

 between the direction of the thermoelectric current and the sign of 

 Hall's coefficient. The anomalous specimen of gold was supplied by 

 Messrs. Johnson and Matthey, by whom its purity was estimated at 

 99 "6 per cent. I do not think that its exceptional behaviour could be 

 accounted for by its physical condition, because, after being succes- 

 sively annealed, raised to a red heat and plunged into cold water, and 

 finally hammered until it was quite hard, it invariably gave the same 

 result. There are, it seems to me, only two possible ways of account- 

 ing for it. Either it behaves as if it were absolutely pure gold, in 

 which case the professedly purer piece of foil, which gave the oppo- 

 site effect, and all the specimens of gold used by Mr. Hall, were 

 affected by impurities ; or it is alloyed with some substance which is 

 capable of reversing the ordinary action of pure gold. Since this 

 specimen was unfortunately in the form of wire, it was impossible to 

 test it for the Hall effect. 



The aluminium, in the form both of foil and of wire, gave opposite 

 effects to those indicated by the sign of Hall's coefficient. I, there- 

 fore, mounted a portion of the foil upon glass, and performed Hall's 



