206 Prof. J. Henry's Contributions 



Section Jl.— Conditions tsoMch injiuence 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 phaenomena 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 



Fig. 3. 



1^ 



a represents coil No. 1, b helix No. 1, and c, d, handles for receiving the 



shock. 



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. 



