41. GASSIOT’S EXPERIMENT. STRIAE. TUBE IN PRIMARY CURRENT. CURRENT VIBRATORY. _Phil. Trans._, ’59, p. 137. _Bakerian Lectures. Phil. Trans._, ’58, p. 1. _Proc. R. So._, x., pp. 36, 393, 404; xii., p. 329; xxiii., p. 356.—The form of tube in which to obtain luminous striae to the best advantage was that of a dumbbell with the electrodes located respectively in the balls—afterwards confirmed by Sir David Solomons, Bart. _Proc. Royal So._, June 21, ’94. _Nature_, Lon., Sept. 13, ’94, p. 490. He obtained in the vacuum luminosity with 500 Daniell’s cells, which he found to be the least E. M. F. that could be employed. He omitted, and apparently overlooked, the introduction of an automatic interrupter in the circuit and the use of a very low E. M. F. § 52. In conjunction with Spottiswoode, 1,080 cells of chloride of silver (about 2,000 volts) were employed, first without, and then with condensers. One of the condensers consisted of the usual tinfoil type, and the other of a self-induction kind, namely of about 1,000 feet of wire. The results were striae with the condensers, and no striae without the condensers. § 8_a_. The results suggested to them that there was some relation in principle between the striae and vibration of the current. They therefore built an ingenious apparatus to test whether this was true or not, and they found such was the case by the following related means. If a current passing directly from the primary battery through the condenser and the discharge tube is undulatory or intermittent in any sense, then it would be able to induce a current in the secondary of the induction coil. § 8 at centre. They found that there was a current thus induced, and they detected it by means of a small discharge tube which became luminous. Fig. 3 p. 17. This was an independent tube near the top of the figure, having nothing to do with the one containing striae, which were produced by the primary current and shown at the right. Dr. Oliver Lodge, F.R.S., in treating of the cathode and X-rays in _The Elect._, Lon., Jan. 31, ’96, p. 438, stated the following with reference to Gassiot’s experiments: “In the days of Gassiot and other early workers (§ 43) on the discharge in rarefied air, it was the stream from the anode that chiefly excited attention. It is this which developed the well-known gorgeous effects which used to be shown at nearly every scientific conversazione.”