He experimented, in January, 1832, on the currents produced by the earth’s rotation--on the 10th at the round pond in Kensington Gardens, and on the 12th and 13th at Waterloo Bridge. [Sidenote: A SPARK FROM A MAGNET.] “This evening,” he writes in his notebook under date February 8, “at Woolwich, experimenting with magnet,[38] and for the first time got the magnetic spark myself. Connected ends of a helix into two general ends, and then crossed the wires in such a way that a blow at _a b_ would open them a little [Fig. 10]. Then bringing _a b_ against the poles of a magnet, the ends were disjoined, and bright sparks resulted.” From succeeding with a steel magnet it was but a short step to succeed when a natural loadstone was used. The next day we find this entry:--“At home succeeded beautifully with Mr. Daniell’s magnet. Amalgamation of wires very needful. This is a natural loadstone, and perhaps the first used for the spark.” He sent to the Royal Society an account of these and the earlier experiments; his paper on terrestrial magneto-electric induction, and on the force and direction of magneto-electric induction, received the distinction of being read as the Bakerian lecture of the year. [Sidenote: TYNDALL’S SUMMARY.] The following summary of this second paper is from the pen of Professor Tyndall:-- He placed a bar of iron in a coil of wire, and lifting the bar into the direction of the dipping needle, he excited by this action a current in the coil. On reversing the bar, a current in the opposite direction rushed through the wire. The same effect was produced, when, on holding the helix in the line of dip, a bar of iron was thrust into it. Here, however, the earth acted on the coil through the intermediation of the bar of iron. He abandoned the bar, and simply set a copper plate spinning in a horizontal plane; he knew that the earth’s lines of magnetic force then crossed the plate at an angle of about 70°. When the plate spun round, the lines of force were intersected and induced currents generated, which produced their proper effect when carried from the plate to the galvanometer. “When the plate was in the magnetic meridian, or in any other plane coinciding with the magnetic dip, then its rotation produced no effect upon the galvanometer.”