206 
Prof. J. Henry’s Contrihutiom 
Section \1,— Conditions *wliich injluence the ^production of 
Secondary Currents, 
26. The secondary currents, as it is well known, were dis- 
covered in the induction of magnetism and electricity, by Dr. 
Faraday, in 1831. But he was at that time urged to the ex- 
ploration of new, and apparently richer veins of science, and 
left this branch to be 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 
induction 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 phaenornena of the secondary galvanic currents. 
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 ensure perfect insula- 
tion ; as often as the circuit of No. 1 was interrupted, a 
powerful secondary current was induced in No. 2. The ar- 
rangement is the same as that exhibited in fig. 3, with the 
exception that in this the compound helix is represented as 
receiving the induction. Instead of coil No. 2. 
29. When the ends of the second coil were rubbed to- 
gether, a spark was produced at the opening. When the 
same ends were joined by the magnetizing spiral (11.), the 
enclosed needle became strongly magnetic. Also when the 
secondary current was passed through the wires of the iron 
horseshoe (12.), magnetism was developed; and when the 
ends of the second coil were attached to a small decomposing 
apparatus, of the kind which accompanies the magneto-elec- 
trical machine, a stream of gas was given off at each pole. 
The shock, however, from this coil is very feeble, and can 
scarcely be felt above the fingers. 
