1897.] HOUSTOX, KEXXELLY — THE PATH OF A CURRENT. 145 



tiiry, the discovery of the voltaic pile brought to the notice of elec- 

 tricians the development of an electric current, or a steadily main- 

 tained discharge. The phenomena produced by the electric current 

 were apparently so different from those produced by electric charges 

 that they were at first believed to be essentially distinct. The elec- 

 tric current could only be produced when a complete conducting 

 path or circuit was provided, any breach of continuity in the con- 

 ducting circuit immediately interrupting the current flow. Conse- 

 quently, it appeared that the electric current passed through the 

 conductor, usually a metallic wire, in a manner somewhat similar to 

 that in which a liquid flows through a pipe. Moreover, the electric 

 current was apparently restricted to the conductor, and could not 

 pass through the insulating medium surrounding it. 



In 1820, not long after the discovery of the voltaic pile. Oersted 

 announced the first known connection between electricity and mag- 

 netism. Using the usual language, when a wire, through which an 

 electric current is flowing, is brought into the neighborhood of a 

 suspended magnetic needle, the poles of the needle are attracted 

 and repelled in a manner depending upon the direction of the cur- 

 rent and its position relatively to the needle. Here an electric 

 current apparently acted at a distance on the needle ; for, in the 

 insulating medium, usually the air, in which the magnet was sus- 

 pended, no electric current could flow, and yet the magnet's poles 

 could be acted upon at a very considerable distance from the wire 

 carrying the electric current. 



Up to the middle of the present century, therefore, the phenom- 

 ena of electricity, magnetism and electromagnetic action, suggested 

 both action at a distance, and that electric currents pass solely 

 through the mass of a conducting wire independently of the exter- 

 nal insulating medium. It is true that the idea of action at a dis- 

 tance was regarded as illogical, and as contrary to the fundamental 

 principles of dynamics, ever since the days of Newton, but despite 

 this unwillingness of physicists, the old notions of actions at a dis- 

 tance continued to be thus passively employed and promulgated, 

 and, even to-day, they still permeate scientific literature. Another 

 reason for the retention of the recognizedly erroneous ideas of 

 action at a distance is to be found in the fact that, up to the middle 

 of this century, all the mathematical processes adopted for dealing 

 with the phenomena of electricity, magnetism and electromagnetic 

 action, tacitly assumed the principles of action at a distance just as 



