The History of Electrical Resonance 



By JULIAN BLANCHARD 



OUR earliest knowledge of electricit}' was of the static kind; later came 

 the voltaic cell and the direct current. Hut not until the discovery 

 of alternating or oscillating currents of electricity could the phenomenon of 

 electrical resonance make its appearance. Today, as we turn the dials of 

 our radio receivers and "tune in" on the station we want it is recognized 

 how widespread its application has become. Nevertheless, it seems that 

 few have given thought to how this important principle came to light and 

 how and when it got into common use. 



The Oscillatory Nature of the Leydex Jar Discharge 



The Leyden jar, discovered in 1746, was for many years one of the most 

 important instruments in the meager equipment of electrical experimenters. 

 When the jar was charged by an electrical machine and the discharging 

 knobs brought close enough together a spark would jump between them. 

 The savants of those days reasoned that this doubly coated jar was a storer 

 of electricity, a condenser; that before the spark passed there was an accu- 

 mulation of positive charge on one coating and of negative on the other; 

 and when the spark passed these charges neutralized each other and the 

 jar was discharged. But they did not know or suspect that this discharge 

 was oscillatory, that first one side and then the other became positively 

 charged, until the motion gradually came to rest. 



The view that such was the case seems tirst to have been put forward in 

 1826 by Felix Savary, in France. It had been observed by him, and very- 

 likely by others as well, that a steel needle magnetized by the discharge of a 

 Leyden jar did not in all circumstances have the same polarity. In the 

 following words he suggested the idea that the results were due to the 

 oscillatory discharge of the jar: 



".\n electric discharge is a phenomenon of movement. Is this movement a 

 continuous translation of matter in a determined direction? Then the opposite 

 polarity of magnetism observed at ditYereiit distances from a straight conductor, 

 or in a helix with gradually increasing discharges, would be due entirely to the 

 mutual reactions of the magnetic particles in the steel needles. 'J'he manner in 

 which the action of a wire changes with its length ap])ears to me to exclude this 

 supposition. 



"Is the electric movement during the discharge, on the other hand, a series of 

 oscillations transmitted from the wire to the surrounding medium and soon attenu- 



415 



