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 magneti%ed; since the introduc- 
tion of this would, in some cases, interfere with the action, and 
tender the results more complex. 
SECTION IL. 
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, b 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- 
