A CENTURY'S PROGRESS IN PHYSICS 339 



charcoal in the circuit, or melt fine wires, and was for 

 some time the most powerful arrangement of its kind. 

 That " galvanism " is something quite different from 

 static electricity was the opinion of many investigators ; 

 Hare considered the heat developed to be the distinguish- 

 ing mark of the electric current. He says: "It is 

 admitted that the action of the galvanic fluid is upon or 

 between atoms ; while mechanical electricity when unco- 

 erced, acts only upon masses. This difference has not 

 been explained unless by my hypothesis, in which caloric, 

 of which the influence is only exerted between atoms, 

 is supposed to be a principal agent in galvanism. " 



Questioning minds were beginning to suspect that 

 there must be some connection between electricity and 

 magnetism. For lightning had been known to make 

 magnets of steel knives and forks, and Franklin had mag- 

 netized a sewing needle by the discharge from a Leyden 

 jar. Finally Oersted of Copenhagen undertook syste- 

 matic investigation of the effect of electricity on the mag- 

 netic needle. His researches were without result until 

 during the course of a series of lectures on "Electricity, 

 Galvanism, and Magnetism M delivered during the winter 

 of 1819-20 it occurred to him to investigate the action of 

 an electric current on a magnetic needle. At first he 

 placed the wire bearing the current at right angles to the 

 needle, with, of course, no result; then it occurred to 

 him to place it parallel. A deflection was observed, for 

 to his surprise the needle insisted on turning until per- 

 pendicular to the wire. 



Oersted's discovery that an electric current exerts a 

 couple on a magnetic needle was followed a few months 

 later by Ampere's demonstration before the French 

 Academy that two currents flowing in the same direction 

 attract each other, while two in opposite directions repel. 

 The story goes that a critic attempted to belittle this dis- 

 covery by remarking that as it was known that two cur- 

 rents act on one and the same magnet, it was obvious 

 that they would act upon each other. Whereupon Arago 

 arose to defend his friend. Drawing two keys out of 

 his pocket he said, "Each of these keys attracts a mag- 

 net; do you believe that they therefore attract each 

 other f" 



