used, a shock is felt each time the
contact with the electromotor is broken, provided the ends of the wire be
grasped one in each hand.

1050. Another effect is observed at the same time, which has long been
known to philosophers, namely, that a bright electric spark occurs at the
place of disjunction.

1051. A brief account of these results, with some of a corresponding
character which I had observed in using long wires, was published in the
Philosophical Magazine for 1834[A]; and I added to them some observations
on their nature. Further investigations led me to perceive the inaccuracy
of my first notions, and ended in identifying these effects with the
phenomena of induction which I had been fortunate enough to develop in the
First Series of these Experimental Researches (1.-59.)[B]. Notwithstanding
this identity, the extension and the results supply, lead me to believe
that they will be found worthy of the attention of the Royal Society.

[A] Vol. v. pp. 349, 444.

[B] Philosophical Transactions, 1832, p. 126.

1052. The _electromotor_ used consisted of a cylinder of zinc introduced
between the two parts of a double cylinder of copper, and preserved from
metallic contact in the usual way by corks. The zinc cylinder was eight
inches high and four inches in diameter. Both it and the copper cylinder
were supplied with stiff wires, surmounted by cups containing mercury; and
it was at these cups that the contacts of wires, helices, or
electro-magnets, used to complete the circuit, were made or broken. These
cups I will call G and E throughout the rest of this paper (1079.).

1053. Certain _helices_ were constructed, some of which it will be
necessary to describe. A pasteboard tube had four copper wires, one
twenty-fourth of an inch in thickness, wound round it, each forming a helix
in the same direction from end to end: the convolutions of each wire were
separated by string, and the superposed helices prevented from touching by
intervening calico. The lengths of the wires forming the helices were 48,
49.5, 48, and 45 feet. The first and third wires were united together so as
to form one consistent helix of 96 feet in length; and the second and
fourth wires were similarly united to form a second helix, closely
interwoven with the first, and 94.5 feet in length. These helices may be
distinguished by the numbers i and ii. They were carefully examined by a
powerful current of electricity and a galvanometer, and fou