INDUCTION OF ELECTRIC CURRENTS. 
127 
9. In these and many other similar experiments no difference in action of 
any kind appeared between iron and other metals. 
10. Two hundred and three feet of copper wire in one length were passed 
round a large block of wood ; other two hundred and three feet of similar wire 
were interposed as a spiral between the turns of the first, and metallic contact 
everywhere prevented by twine. One of these helices was connected with a 
galvanometer, and the other with a battery of one hundred pairs of plates four 
inches square, with double coppers, and well charged. When the contact 
was made, there was a sudden and very slight effect at the galvanometer, and 
there was also a similar slight effect when the contact with the battery was 
broken. But whilst the voltaic current was continuing to pass through the 
one helix, no galvanometrical appearances of any effect like induction upon the 
other helix could be perceived, although the active power of the battery was 
proved to be great, by its heating the whole of its own helix, and by the bril- 
liancy of the discharge when made through charcoal. 
1 1 . Repetition of the experiments with a battery of one hundred and twenty 
pairs of plates produced no other effects ; but it was ascertained, both at 
this and the former time, that the slight deflection of the needle occurring 
at the moment of completing the connexion, was always in one direction, and 
that the equally slight deflection produced when the contact was broken, was 
in the other direction ; and also, that these effects occurred when the first 
helices were used (6. 8.). 
12. The results which I had by this time obtained with magnets led me 
to believe that the battery current through one wire, did, in reality, induce a 
similar current through the other wire, but that it continued for an instant 
only, and partook more of the nature of the electrical wave passed through 
from the shock of a common Leyden jar than of that from a voltaic battery, 
and therefore might magnetise a steel needle, although it scarcely affected the 
galvanometer. 
13. This expectation was confirmed; for on substituting a small hollow helix, 
formed round a glass tube, for the galvanometer, introducing a steel needle, 
making contact as before between the battery and the inducing wire (7. 10.), 
and then removing the needle before the battery contact was broken, it was 
found magnetised. 
