218 PROCEEDINGS OF THE AMERICAN ACADEMY. 



IX. 

 WAVE LENGTHS OF ELECTRICITY ON IRON WIRES. 



By Charles E. St. John, A. M. 



Presented by Professor John Trowbridge, May 9, 1894. 



Since the experimental demonstration of the existence of the oscil- 

 lating electric discharge, it has been an interesting field of investiga- 

 tion to ascertain whether the magnetization of iron and nickel can 

 follow such rapidly alternating impulses as are obtained by the oscil- 

 lating discharge of a condenser through a circuit of low self-induction, 

 and, if magnetization does follow, in what way and to what extent 

 can it affect the character of an electric wave propagated along wires 

 of masfnetic material. 



The results of investigation have shown considerable disagreement, 

 as will be seen from the following brief resume of the investigations 

 bearing upon these points. The questions referred to did not dis- 

 tinctly appear in all the investigations, as they have arisen since ; but 

 results were obtained and published which directly relate to at least 

 one of the points under consideration. 



M. Savary announced, as early as 1826, that, when a needle was 

 placed in a spiral through which a Leyden jar was discharged, rever- 

 sals of polarity were obtained by varying the quantity of discharge 

 through the spiral ; and Faraday * adduces the magnetizing of needles 

 and bars by common (static) electricity as evidence of its identity 

 with Voltaic electricity, and in his ex[)eriment to show that common 

 electricity can deflect the magnetic needle, when a Leyden battery is 

 discharged through the galvanometer, he states the fact that the mag- 

 netism of the needle may be removed or reversed by the discharge. 



Professor Henry f repeated the experiments of Savary with great 

 skill and care. He obtained reversals of polarity by increasing 

 the quantity of electricity discharged through the spiral in which the 

 needlp was placed, while the direction of the discharge remained the 

 same, and by varying the distance between the primary and secondary. 



* Experimental Researches on Electricity. 1833. 

 t Writings of Joseph Henry, p. 201. 1842. 



