From Sciagraph of Knee-joint. Straight, Front View.By Prof. Goodspeed.Photo. Times, July, ’96.
From Sciagraph of Knee-joint. Straight, Front View.By Prof. Goodspeed.Photo. Times, July, ’96.
From Sciagraph of Knee-joint. Straight, Front View.By Prof. Goodspeed.Photo. Times, July, ’96.
It might be argued, that in as much as zinc would reflect only about three per cent. of the incident rays, no practical gain wouldensue in sciagraphy by the use of a reflector. He pointed out the falsity of such an argument. In the first place, the angle employed in these tests was 45°. With greater angles, the proportion of reflected rays would be greater assuming that the law of reflection is the same as that of light. By mathematical calculation and tests, he showed that there was no doubt whatever about the advantage of using reflectors. He obtained a sciagraph, on a single plate, of the ribs, arms and shoulder, clearly represented. He stated the details as follows. “A funnel shaped zinc reflector two feet high, with an opening of five inches at the bottom and 23 inches at the top, was used in the experiment. A tube similar in every respect to those previously described, was suspended in the funnel, so that only the static screen of the tube was above the former. The exact distance from the electrode to the sensitive plate was four and one-half feet.”
147.Discharge Tube Placed in Oil.—When theE. M. F.was increased, by having the discharge tube, as usual, in open air, sparks formed behind the electrode, and within the vacuum, and endangered the life of the discharge tube. He obviated this difficulty partly by having the electrode located well within the evacuated space, so that the wire leading to it was unusually long. By excessiveE. M. F., also, streamers broke out at the end of the tube. To overcome all difficulties in connection with sparking and breaking of the tube, he followed the proposition of Prof. Trowbridge, and submerged the discharge tube in oil,§ 11, at end, and§ 13, which was continually renewed by flowing into and out of the vessel in which the discharge tube was contained, all as shown in the accompanying figure, p.157, “Discharge Tube Immersed in Oil.” The discharge tube,t, may be recognized by its shape, and it is located horizontally in a cylindrical tube lying sidewise upon a table. To regulate the flow of the oil, the reservoir may be raised and lowered by a bracket, s. The X-rays enter the outside atmosphere by passing first through glass, then oil, and then through a diaphragm of “pergament” forming the right hand end of the oil vessel. When the results were compared with those obtained by Roentgen in his first experiments, the rays were found so powerful that it is not surprising that Tesla was able to obtain more definitely a closer knowledge of the properties of the rays. Roentgen obtained, with his tube and a screen of barium platino cyanide, a shadow picture of the bones of the hand at a distance of less than 7 ft., while Tesla obtained a similar picture with a screen of calcic tungstate, and withhis tube immersed in oil at a distance of 45 ft. Tesla also made sciagraphs with but a few minutes’ exposure at a distance of 40 ft., by the help of Prof. Henry’s method,i.e., with the assistance of a fluorescent powder.§ 151. He referred also to Salvioni’s suggestion of a fluorescent emulsion. He attributed to Mr. E. R. Hewitt the conjecture that the sharpness of the sciagraphs might be increased by a thin aluminum sheet having parallel groves. Several experiments were made, therefore, with wire gauze, as well as with a screen formed of a mixture of fluorescent and iron-fluorescent powders. With the strong power of the rays as obtained by Tesla in combination with such adjuncts, the shadows were sharper, although the radiation, of course, was weakened by the obstruction.§ 107b.
Discharge Tube Immersed in Oil,§ 147,Page156.
Discharge Tube Immersed in Oil,§ 147,Page156.
Discharge Tube Immersed in Oil,§ 147,Page156.
With the apparatus involving the discharge tube in oil, and with tremendously high potential, he obtained what may be called wonderful results; for with the sciascope he obtained shadow pictures of the vertebral column, outline of the hip bones, the location of the heart (and later detected its pulsations), ribs and shorter bones, and, without the least difficulty, the bones of all the limbs. More than this, a sciagraph of the skeleton of the hand was perceived through copper, iron or brass very nearly 1/4 inch thick, while glass 1/2 inch thick scarcely dimmed the fluorescence. The skull of the head of an assistant acted likewise, while at a distance of three feet from the discharge tube. The motion of the hand was detected upon the screen althoughthe rays first passed through one’s body. In making observations with the screen, he advised that experimenters should surround the oil box closely, except at the end, with thick metal plates, to prevent X-rays from coming in undesired directions by reflection from different objects in the room. Obviously the shadows will be sharper.
148.Bodies Not Made Conductors by X-rays.Tesla referred to Prof. J. J. Thomson as having announced some time ago “that all bodies traversed by Roentgen radiations become conductors of electricity.” The author has witnessed other similar expressions giving credit to Thomson in this respect, but he understands that Prof. Thomson, having discovered that X-rays discharge both negatively and positively charged bodies, conjectured or drew a corallary as to the probability of the bodies therefore becoming conductors. Tesla, nevertheless, seems to have proved that the corallary does not hold. In the first place he employed the very powerful rays, and next, he let the oil be the substance traversed by the rays. Besides this, he applied a sensitive resonance test. See detail treatment of his experiments on this subject inElect. Rev., N.Y., June 24, ’93, p. 228. In brief “a secondary not in very close inductive relation to the primary circuit, was connected to the latter and to the ground, and the vibration through the primary was so adjusted that true resonance took place. As the secondary had a considerable number of turns, very small bodies attached to the free terminal produced considerable variations of potential of the latter. Placing a tube in a box of wood filled with oil and attaching it to the terminal, I adjusted the vibration through the primary so that resonance took place without the bulb radiating Roentgen rays to any appreciable extent. I then changed the conditions so that the bulb became very active in the production of the rays.”
According to the corallary above referred to, the oil should be, with such an environment and under such subjection, a conductor of electricity, but it was not. He emphasized his satisfaction in the results by saying “the method I followed is so delicate that a mistake is almost an impossibility.”
Prof. W. C. Peckham,Elect. World, N.Y., May 30, ’96, reasoned that the oscillating electro-static action upon the outside of the tube, is concerned in the production of fluorescence, and other properties of X-rays. “These oscillations are certainly synchronous with the vibrations of the cathode rays in the tube, which in turn synchronize with the oscillation in the induction coil. If the vibrations of the tube cannot keep time with those of its coil, few or no X-rays will be given out. The cause seems tobe similar to that of sympathetic vibrations in sound. In a word, the discharge tube is a resonator for its coil, and when the coil and tube are properly attuned, the maximum effect is obtained.
149.Appleyard’s Experiment. Non-conductors Made Conductors by Current.Proc. Phil. So., May 11,Nature, Lon., May 24, ’64, p. 93. A piece of celluloid was pressed between two metal plates serving as terminals. A galvanometer was employed to indicate the diminution of resistance by time, and it also showed that the electrification was negative. When mercury was one of the metals, the abnormal results did not occur, except to a very small extent. When the celluloid was replaced by gutta percha tissue, the electrification was normal. Many non-metals were employed, and several were lowered in resistance.
149a.Resistance Somewhat Independent of Metal Particles.—Through a mixture of conducting and non-conducting materials, like a sheet of gutta percha, having brass filings imbedded therein,—with 750 volts, no current passed, and this held true until the proportion in weight of the metal to the gutta percha was 2 to 1. Let it be remembered, also, that selenium is reduced as to resistance under the influence of light.
150.Minchin’s Experiment. Resistance Lowered by Electro-magnetic Waves.Nature, Lon., May 24, ’94, p. 93.—Referring to Appleyard’s experiment, it will be noticed that he found that mixtures of certain limited per cents. of metallic particles and insulators were exceedingly high in resistance. Prof. G. M. Minchin found that such materials became conductors under the influence of powerful electro-magnetic disturbances, and that after the current was conducted, its resistance remained greatly lowered in behalf of very weak impulses, although, before the experiment, the resistance was so high.§ 14a. But after the current was interrupted by moving the terminal away from the mixture, the high resisting power returned slowly, at a rate somewhat in proportion to the hardness of the mixture. The film employed consisted of shellac or gelatine or sealing wax, while among the metals was pulverized tin. In the latter case, the resistance was reduced by the electro-magnetic waves from apparent infinity to 130 ohms, the electrodes being displaced by 1 cm.