galvanometer.

9. In these and many 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 coiled
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 coil, 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 nor 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 brilliancy of the discharge when made
through charcoal.

11. 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 the current 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.

14. When the battery contact was first made, then an unmag