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VI

28. Davy, Bancalari and Quet’s Experiments. Electric Arc, Magnetism and Flame. Sound Produced. Practical Application of Electric Arc. Phil. Mag., 1801.—When the electric arc, for example between two carbon electrodes, occurs, in a powerful magnetic field, it is violently drawn to one side as first shown by Sir Humphry Davy, as if the wind were blowing it and sometimes it is broken into two parts. Fig. VI. Again a loud noise is produced. ssss1. Without the magnet, the appearance is as at the left. With the energized magnet, the arc and light, as a whole, are as shown at the right.

29. De La Rive’s Experiment. Rotation of Luminous Effect by Magnet. Application to Explain Aurora Borealis. Phil Trans., vol. 137, 1847. Pynchon, p. 471. Ganot, Sect. 928.—An oval discharge tube was employed, having a highly exhausted atmosphere (for those days) of spirits of turpentine. A cylindrically shaped pole of a magnet extended into the bulb half way, Fig. 4, p. ssss1. The inner end of the magnetic pole formed one electrode of the tube, and the other electrode was a ring within the vacuum at the foot of the magnetic pole. A fountain of light extended from one end of the magnet pole to the other, and remained stationary, while the magnet was not energized; but the light was condensed into an arc and travelled around the magnet pole when a current was passed through the coils of the magnet. For similar action of magnet on a flexible and movable wire carrying a current, see experiments of Spottiswoode and Stokes, Proc. R. So., 1875. The aurora borealis rotates around the pole of the earth, and therefore, De La Rive thought that the phenomenon in his laboratory and in nature were but one and the same thing and different only in degree. He also extinguished an arc in open air by means of a powerful magnet.