On Electro-Dynamic Induction. 



215 



contact of two spires is sometimes sufficient to neutralize the 

 whole effect. 



25. It must be recollected that all the experiments with these 

 coils and helices, unless otherwise mentioned, are made without 

 the reaction of iron temporarily magnetized ; since the introduc- 

 tion of this would, in some cases, interfere with the action, and 

 reader the results more complex. 



SECTION II. 



Conditions which influence the production of Secondary Currents. 



26. The secondary currents, as it is well known, were discov- 

 ered in the induction of magnetism and electricity, by Dr. Fara- 

 day, in 1831. But he was at that time urged to the exploration 

 of new, and apparently richer veins of science, and left this branch 

 to be farther traced by others. Since then, however, attention 

 has been almost exclusively directed to one part of the subject, 

 namely, the induction from magnetism, and the perfection of the 

 magneto-electrical machine. And I know of no attempts, except 

 my own, to review and extend the purely electrical part of Dr. 

 Faraday's admirable discovery. 



27. The energetic action of the flat coil, in producing the in- 

 duction of a current on itself, led me to conclude that it would 

 also be the most proper means for the exhibition and study of the 

 phenomena of the secondary galvanic currents. 



Fig. 3. 



a coil No. 1, h helix No. 1, and c, d, handles for receiving the shock. The plate 

 of glass is omitted in the drawing. 



28. For this purpose coil No. 1 was arranged to receive the 

 current from the small battery, and coil No. 2 placed on this, with 

 a plate of glass interposed to insure perfect insulation ; as often as 

 the circuit of No. 1 was interrupted, a powerful secondary current 

 was induced in No. 2. The arrangement is the same as that ex- 



