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. 17. 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. [Illustration: VII ] 30. PLÜCKER AND HITTORF’S EXPERIMENTS. ACTION OF MAGNET ON CATHODE COLUMN OF LIGHT. _Pogg. Ann._, 1858 and 1869. Plücker found that the magnet acts on the cathode light in a rarefied atmosphere in a different manner from that on the anode light. In the former the light follows the magnetic curves and strike the side of the bulb, according to position of the poles, see Fig. VII. “Where the discharge is perpendicular to the line of the poles, it is separated into two distinct parts, which can be referred to the different action exerted by the electro-magnet on the two extra currents produced in the discharge.” _Ganot._ § 925.