3. FIZEAU’S EXPERIMENT. SPARK IN SECONDARY INCREASED BY CONDENSER IN PRIMARY, 1853. _Pynchon_, p. 456.—He connected the plates of a condenser respectively to the terminals of an automatic circuit breaker in the primary circuit, and noticed that the sparks between the two terminals of the interrupter produced by the self-induced current were greatly diminished, while those of the secondary coil were about double in length. Since that time it has been universally customary to equip induction coils with condensers in like manner.
4. VINCENTINI’S EXPERIMENT. CONDITION OF A GAS AROUND A LIVE WIRE. _Nuovo Cimento_, Vol. XXXVI., No. 3. _Nature_, Lon., March 28, ’95, p. 514. _The Elect._, Lon., Feb. 8, ’95, p. 433. G. Vincentini and M. Cinelli found that the molecules of a gas at and near the surface of a platinum wire, rendered incandescent by a current, are electrified, and that with hydrogen their potential is about .025 volt above the mean potential of the wire. With air and carbonic acid gas the increment is about 1 volt. The apparatus, Fig. II., consists essentially of means for passing a current along a platinum wire, a bulb for preventing draughts, and an electrometer having a platinum disc electrode that could be adjusted to different positions. It was noticeable that the electrification did not reach a maximum instantaneously upon closing the current through the wire, but the time was less at points below the wire than above.
5. HENRY’S EXPERIMENT. MAGNETIZING RADIATIONS FROM AN ELECTRIC SPARK. _Proc. Inter. Elect. Cong._, 1893, p. 119. Preece alluded to Prof. Henry’s original experiment illustrating the action of an electric discharge § 2 at a distance. He placed a needle in the cellar. Disruptive discharges of a Leyden jar at 30 ft. distant, in an upper room, produced a magnetic effect upon the needle.
6. FARADAY’S EXPERIMENT. ARC MAINTAINED BY CERTAIN METALLIC ELECTRODES AT LOW VOLTAGE. _Experimental Researches. Phil. Trans._, _Se._ IX., Dec., 1894. § 107. to 1078. The generator employed in this experiment consisted of a few cells of a chemical battery, and he obtained, what he called, a voltaic spark. He observed that when the two terminals touched each other, a burning took place and an appearance as if the spark were passing on making the contact, the terminals being pointed and formed of metal. When mercury was the terminal, the luminosity of the spark was much greater than with platinum or gold, although the same quantity of current passed in both cases. He attributed the difference to a greater amount of combustion in the case of mercury, than in those of gold and platinum. He obtained almost a continuous spark by bringing down a pointed copper wire to the surface of mercury and withdrawing it slightly. Wheatstone, in 1835, analysed the light of sparks, and found them to be so characteristic that by means of the prism and the spectra formed, the metal could be known.