40. De La Rue and Müller’s Experiment. Striae. Black Prints on Walls of Tube. Phil. Trans., 59, ’78.—Particles of the metal of the electrodes were deposited upon the inside of the glass forming permanent black striae or bands [§ 44], at points corresponding to the spaces between the luminous striae. [§ 6]. near the end.
CHAPTER IV
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. [§ 8a]. 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.”
42. Poggendorff’s Experiment. Effects of Interrupting a Current Within Discharge Tube. Phil. Mag., 4th Se., vol. x., 1855, p. 203-207.—Imagine an electric bell vibrator and magnet within the glass receiver upon an air pump. Upon connecting the magnet and vibrator in series with a small electric battery, it is evident that in the open air, as usual in electric bells, there will be a minute violet spark at the terminals of the circuit breaker. [§ 6]. Now, let the air be exhausted as far as possible by means of a mechanical pump as constructed in 1855. Poggendorff performed such an experiment, and he noticed that in the poor vacuum the ordinary violet spark became yellow, while blue light like a small enveloping tube surrounded the hammer of the vibrator and wire leading to the opposite contact and a little projection extending away from the hammer. His experiment was unique, because showing for the first time that a current from a battery, if interrupted in the vacuum, will not only produce the usual minute spark, but that a blue tube of light will be produced around the conductors within the vacuum.
43. De La Rue and Müller’s Experiment. Source of the Striae at the Anode. Number of Striae Varied by Change of Current. Phil. Trans., 1878.—By an arrangement of means for causing different pressures, they made a discovery, namely, that as far as the eye is concerned the striae begin to have their existence at the anode. [§ 46]. Imagine the internal gas pressure to become less and less. First, a violet luminosity occurs around the anode as in [§ 42]. As the pressure becomes less and less, luminous striae move toward the cathode accompanied by more and more striae, which increase either to form a column reaching a certain distance or else extending through the whole distance between the electrodes. [§ 46]. They observed that when the E. M. F. was constant and the current changed, the variation in the appearance of the striae was very regular. [§ 41]. With some tubes the number of striae increased with the increase of current, while with a decrease of current the number of striae became less and less. [§ 8a]. With some tubes the number of striae increased while the current decreased. [§ 8a]. With the use of a condenser, then as the E. M. F. decreased together with a diminution of current, the number of striae varied. The striae nearest the anode vanished first, as they diminished in number with the fall of the E. M. F. The striae on the other hand originated at the anode, when the charge of the condenser was gradually increased from a minimum, and then the striae continued to increase from the anode as the source. As to the color of the striae, the same was changed by an alteration of the current.
44. Solomons’ Experiment. Dark Bands by Small Discharges. Nature, Lon., Sept. 13, ’94. Proc. R. So., June 21, ’94.—Solomons found that in a very dark room, striae (alternate light and darkness) appeared with very minute discharges, and as the current was increased, they vanished, appearing again when the discharge was strong. He could not obtain them until the luminous column extended to the glass forming the large glass tube. [§ 40].
45. Spottiswoode’s Experiment. Governing the Motion of Striae. Effect Upon Motion by Diameter of Discharge Tube. Motion Stopped by Magnet. Proc. R. So., vol. 33, p. 455.—Spottiswoode found that he could obtain motion when he desired. He introduced some constant resistances and also a rheostat of fine adjustment. The least change of resistance caused some effect upon the striae. The general principle that he established was that letting it be assumed that the striae are stationary then; “An increase of resistance produces a forward flow, and a decrease of the resistance a backward flow,” differences of as little as 1 ohm in the primary current caused the effect. Sometimes the velocity of the flow is fast and sometimes slow, being so rapid in certain instances that the unaided eye cannot distinguish them, but they are known to exist by the use of the revolving mirror. [§ 46]. With tubes of small diameter, compared with their length, he noticed the fact that the striae in one portion of the tube moved faster than those in another portion. [§ 46]. Sometimes one group moved while the other one was stationary. Sometimes they moved in opposite directions. This last named phenomenon occurred also in very wide tubes. The points at which the charge took place he called nodes. He discovered external means for stopping this action. He did it by means of a magnet located opposite one end of the tube. [§ 31]. When the magnet was energized, all motion ceased. [§ 31].
