31. THOMSON’S EXPERIMENT. A DISCHARGE RETARDED ACROSS AND ACCELERATED ALONG THE LINES OF MAGNETIC FORCE. _Nature_, Lon., Jan. 31, 1895, p. 333. _Lect. Royal Inst._—Prof. J. J. Thomson, F. R. S., performed an experiment which illustrates that the electrical discharge is retarded in flowing across the lines of magnetic force and accelerated in flowing with or parallel to such lines. As illustrated in Fig. 20, p. 17, he employed a large electro-magnet adapted to be cut in and out of circuit. He had two air chambers, one a bulb, indicated by a circle, and the other a tube bent into a rectangle, indicated by the dotted square. Between these, was an adjustable coil having its terminals connected to the outside coatings of Leyden jars. When the discharge took place between the poles of the magnet, that is, in the direction of the lines of force, the discharge was helped along by the magnetic field, but when it took place across the bulb, that is, across the lines of force, the discharge was retarded. “The coil can be adjusted so that when the magnet is ‘off’ the discharge passes through the bulb, but not round the square tube; when, however, the magnet is ‘on,’ the discharge passes in the square tube but not in the bulb.” [Illustration: SOME EXPERIMENTS PRIOR TO LENARD’S. ] 32. THOMSON’S EXPERIMENT. RESISTANCE OFFERED TO STRIAE BY A THIN DIAPHRAGM. _Lect. Royal Inst. Nature_, Lon. Jan. 31, ’95, p. 333.—It has often been remarked that lightning always takes the easiest path. The same has been noticed with references to the artificial electric spark. Prof. J. J. Thomson, F.R.S. performed an experiment, which not only confirms this principle but does so in an emphatic manner, and proves it true in reference to the electric discharge in rarefied gases. He arranged a very thin platinum diaphragm so as to divide a Geissler tube into two compartments, Fig. 19, p. 17. He then formed a passage way around the diaphragm, which could be opened and closed by mercury, by respectively lowering and raising the lower vessel of mercury along the barometer tube. When the passage way is opened around the diaphragm, the luminosity extends through the passage way in preference to going through the diaphragm. When the passage way is closed by mercury, the discharge goes through the thin metal plate. The same was found to occur when the platinum leaf was replaced by a mica scale. 33. SIR DAVID SOLOMON’S EXPERIMENT IN 1894. _Proc. Royal So._, June 21, ’94. _Nature_, Lon. Sept. 13, ’94, p. 490.—With a tube having a perforated diaphragm, he noticed a “forcing effect” at and near the hole. The striae had the appearance of being pushed through from the longer part of the tube—the diaphragm not being in the centre. There was no passage way around the diaphragm—only through the small puncture. § 19. [Illustration] ------------------------------------------------------------------------ CHAPTER III