[A] Philosophical Transactions, 1831, p. 202.

S 6. General remarks and illustrations of the Force and Direction of Magneto-electric Induction.

193.  In the repetition and variation of Arago’s experiment by Messrs. Babbage, Herschel, and Harris, these philosophers directed their attention to the differences of force observed amongst the metals and other substances in their action on the magnet.  These differences were very great[A], and led me to hope that by mechanical combinations of various metals important results might be obtained (183.).  The following experiments were therefore made, with a view to obtain, if possible, any such difference of the action of two metals,

  [B] Philosophical Transactions, 1825, p. 472; 1831, p.78.

194.  A piece of soft iron bonnet-wire covered with cotton was laid bare and cleaned at one extremity, and there fastened by metallic contact with the clean end of a copper wire.  Both wires were then twisted together like the strands of a rope, for eighteen or twenty inches; and the remaining parts being made to diverge, their extremities were connected with the wires of the galvanometer.  The iron wire was about two feet long, the continuation to the galvanometer being copper.

195.  The twisted copper and iron (touching each other nowhere but at the extremity) were then passed between the poles of a powerful magnet arranged horse-shoe fashion (fig. 32.); but not the slightest effect was observed at the galvanometer, although the arrangement seemed fitted to show any electrical difference between the two metals relative to the action of the magnet,

196.  A soft iron cylinder was then covered with paper at the middle part, and the twisted portion of the above compound wire coiled as a spiral around it, the connexion with the galvanometer still being made at the ends A and B. The iron cylinder was then brought in contact with the poles of a powerful magnet capable of raising thirty pounds; yet no signs of electricity appeared at the galvanometer.  Every precaution was applied in making and breaking contact to accumulate effect, but no indications of a current could be obtained.

197.  Copper and tin, copper and zinc, tin and zinc, tin and iron, and zinc and iron, were tried against each other in a similar manner (194), but not the slightest sign of electric currents could be procured.

198.  Two flat spirals, one of copper and the other of iron, containing each eighteen inches of wire, were connected with each other and with the galvanometer, and then put face to face so as to be in contrary directions.  When brought up to the magnetic pole (53.).  No electrical indications at the galvanometer were observed.  When one was turned round so that both were in the same direction, the effect at the galvanometer was very powerful.