80 ME^rORIAL OF JOSEPH HENRY. 



polarities at their extremities, suggested a strong analogy to magnetic 

 action, and led in many minds to the thought amounting almost to 

 to a conviction that there existed an inherent connection between 

 electricity and magnetism. 



The attempts to discover this connection had been made with 

 galvanic piles or batteries whose poles were not connected by con- 

 ductors, under the expectation that these would show magnetical 

 relations, although in such cases the electricity, accumulated at the 

 extremities, was evidently stagnant. It was reserved for Oersted 

 first to bring into prominent view the fact that it was not while 

 the electricity was thus at rest, but while it was flowing through 

 the wire connecting the two poles, that it exhibited magnetic action, 

 and that a wire thus carrying a current — while it had the power of 

 affecting a magnetic needle, was in turn susceptible of being acted 

 on by a magnet ; and this was the initial step in the science of 

 electro-magnetism. 



The announcement of this discovery in 1820 at once brought into 

 the field a host of experimenters, repeating and extending the obser- 

 vations of Oersted, and by various methods of research multiply- 

 ing the proofs of the magnetic relations of the voltaic currents. 

 Soon Arago and Davy discovered the magnetizing power of the 

 voltaic Conductor on iron filings, and the former found that when a 

 soft iron wire was placed in a conducting helix it became a tempo- 

 rary magnet as long as the current was maintained. Now came 

 forward to take part in these investigations one who was at the same 

 time a distinguished mathematician and a great experimenter, a 

 combination which is to be regarded as the consummation of power 

 in the investigation and discovery of natural laws. 



The French philosopher Ampere, here referred to, made the 

 momentous discovery that when two wires are conveying currents 

 in the same direction they mutually attract, but that when these 

 currents flow in opposite directions the conducting wires repel. 



