Cooling Discharge Tube. Edison. [§ 135].
CHAPTER XI
137. Tesla’s Experiments. Elec. Rev., N.Y., March 11, ’96, page 131, March 18, page 147, April 1, page 171, and April 8, page 183. Kind of Electrical Apparatus for Operating Discharge Tubes for Powerful X-rays. [§ 106], [109], [114], [131]. The experiments performed by Nikola Tesla were particularly noteworthy for the magnitude and intensity of the rays generated by his apparatus, under his skilful manipulation of the adjustments and circuits particularly as to resonance. The remarkable results that he obtained are not surprising when we learn that he employed his well-known system for producing exceedingly enormous potential and unusually high frequency. [§ 51]. The primary electrical generator as he indicated and as apparent from his system referred to in the above section, could be either a direct or alternating current generator, or other form. If the first is employed, of course an interrupter is necessary in order that there may be a current induced in the secondary.
Sciagraph of Rat, Taken by Oliver B. Shallenberger with Focus tube
(CUT AT p. [81]) and Tesla System. [§ 137], pp. [136] and [138].
Mr. Oliver B. Shallenberger, (Mem. Amer. Inst. Elec. Eng.) whose laboratory is in Rochester, Pa., gave some important general instructions concerning the Tesla system [§ 51], that he employed in the production of remarkably clear sciagraphs, in conjunction with the focus tube, [§ 91], representing the hand at page 68, and showing a rat shown at this [§ 137]. (Elec. World, N.Y., March 17, ’96.) Even the ligaments were clearly shown in the sciagraph of the rat, and some of them are dimly reproduced by the half tone process. As to the apparatus and operation, which are especially important, it may be stated that the current was taken from an alternator, of a frequency of 133 periods per second, and passed through a primary coil of a transformer for increasing the E. M. F. from 100 volts to from 16 to 25 thousand. The secondary current was then passed through Leyden jars and a double cascade of slightly separated brass cylinders, whereby it was changed into an oscillatory current of an extremely high frequency, which was then conducted through the primary of a second induction coil having very few turns of wire, and no iron core and having a ratio of 7 to 1. By this means the E. M. F. was raised to somewhere between 160,000 volts to 250,000, and was used to energize the discharge tube for the generation of X-rays. Caution should be taken, because the current coming from the first transformer, being of large quantity and very high E. M. F. is exceedingly dangerous, but the current of the second secondary has been passed through one’s body without danger, as reported by Mr. Tesla several years ago, and confirmed by Mr. Shallenberger.
138. Phosphorescent Spot Maintained Cool.—In testing the power of the X-rays in connection with the appearance of the phosphorescent spot, Tesla noticed that they were most powerful when the cathode rays caused the glass to appear as if it were in a fluid state. [§ 61]. To prevent actual puncture, he maintained the spot cool by means of jets of cold air. It became possible thereby to use bulbs of thin glass at the location of the generation of the X-rays. [§ 119]. He concluded from certain results that not only was glass a better material for discharge tubes than aluminum, but because, by other tests, he found that thin aluminum cast more shadow with X-rays than thicker glass. There are, of course, many other reasons, based on mechanical construction, why glass is preferable, and also why a tube with an aluminum window is not to be desired. Principally, the latter will soon leak.
139. Expulsion of Material Particles through the Walls of a Discharge Tube.—At quite a low vacuum, and after sealing off the lamp, he attached its terminal to that of the disruptive coil. After a while, the vacuum became enormously higher, as indicated by the following steps: First, a turbid and whitish light existed throughout the bulb. This was the first principal characteristic. Next, the color changed to red, and the electrode became very hot, in that case where powerful apparatus was employed. The precaution should be taken to regulate the E. M. F., to prevent destruction of the electrode. Gradually, the reddish light subsided, and white cathode rays, which had begun, grew dimmer and dimmer until invisible. At the same time, the phosphorescent spot became brighter and brighter and hotter and hotter, while the electrode cooled, until the glass adjacent thereto was uncomfortably cold to the touch. At this stage, the required degree of exhaustion was reached, and yet without any kind of a pump. He was enabled to hasten the process by alternate heating and cooling, and by the use of a small electrode. This whole phenomenon was exhibited with external electrodes as well. He acknowledged that instead of the disruptive coil, a static machine could be used, or, in fact, any generator or combination of devices adapted to produce a very high E. M. F.