1049.  The inquiry arose out of a fact communicated to me by Mr. Jenkin, which is as follows.  If an ordinary wire of short length be used as the medium of communication between the two plates of an electromotor consisting of a single pair of metals, no management will enable the experimenter to obtain an electric shock from this wire; but if the wire which surrounds an electro-magnet be 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 found to have no communication with each other.

1054.  Another helix was constructed upon a similar pasteboard tube, two lengths of the same copper wire being used, each forty-six feet long.  These were united into one consistent helix of ninety-two feet, which therefore was nearly equal in value to either of the former helices, but was not in close inductive association with them.  It may be distinguished by the number iii.