Dr. Faraday concluded that there is no real attraction or repulsion between the wire and either pole of a magnet, the action which imitates these effects being of a compound nature; and he also inferred that the wire ought to revolve round a magnetic pole of a bar magnet, and a magnetic pole round a wire, if proper means could be devised for giving effect to these tendencies, and for isolating the operations of a single pole. For the first idea of electro-magnetic rotation the world is indebted to Dr. Wollaston; but Dr. Faraday, with his usual ingenuity, was the first who carried out the theory practically. The rotation of a wire (conveying a current of voltaic electricity) round one of the poles of a magnet is well displayed with the simple contrivance devised by him. (Fig. 203.) [Illustration: Fig. 203. N. A small bar magnet cemented into a wine-glass, the north pole being at N. A is a moveable wire looped over the hook, which is the positive (+) pole of the battery; the free extremity rotates round the pole of the magnet when the current of electricity passes. The dotted line represents the level of the mercury which the glass contains. The electricity passes in at A, and out at the wire B, as shown by the arrows. C is connected with the negative, and D with the positive, pole of the battery.] By a careful observation of the complex action of an electrified wire upon a magnetic needle, Dr. Faraday was enabled to analyse the phenomena with his usual penetration and exhaustive ability, and he found, as Daniell relates,--