The author performed some experiments (Elect. Eng., N.Y., Apr. 15, ’96, p. 379) in relation to candle-power of X-rays by looking into a sciascope and moving it away until the luminosity just disappeared. He then detached the black paper cover from the phosphorescent screen and pointed the sciascope toward a candle flame and receded away until the fluorescence also disappeared. The distances, with different candles, would, of course, somewhat vary, but it would in the rough be a constant quantity, while different discharge tubes would cause the vanishing fluorescence at different distances. Now, assuming that the X-rays vary inversely as the square of the distance, as believed by Röntgen, their power to fluoresce could, therefore, always be named as so much of a candle-power.
105. Simple Device for Comparing and Locating the Source and Direction of X-rays. Phosphorescence Not Essential.—In the ordinary sciascope, the fluorescent screen is located at one end, and the eyehole at the other. He modified this construction by employing a long straight tube, made of thick metal, so that X-rays could not enter through the wall. About at the centre of the tube was a diaphragm of a fluorescent material. Now, it is evident that if this is directed toward the phosphorescent spot and placed very close to the same, and the other end be looked into, the screen will become fluorescent, if X-rays are emitted from the area expected. Such a result occurred. With this instrument, he was able to show, in a similar way, that X-rays did not come from the anode, nor from the cathode directly. In one case, he provided a piece of platinum within the discharge tube, in such a position as to be struck by the cathode rays. [§ § 91] and [116]. The instrument showed that X-rays radiated from the platinum, although the latter was not luminous nor phosphorescent,—illustrating again that phosphorescence is not a necessary accompaniment of X-rays, and assisting in upholding the principle that as the phosphorescence diminishes by increase of vacuum and increase of E. M. F., the X-rays increase. It should be noticed that Prof. Thomson emphasizes that the tube should be made of thick metal.
106. Rice’s Experiment. Apparatus for Obtaining X-Rays. [§ 109], [114], [131], [137]. Tube Energized by a Wimshurst Machine. Elect. Eng., N.Y., Apr. 22, p. 410.—Roentgen had always employed the induction coil. As to those who first excited the discharge tube by the Holtz or Wimshurst machine or generators of like nature, it is not certain; but, according to public records, they were independently Prof. M. I. Pupin, of Columbia College, and Dr. William J. Morton, of New York. See Electricity, N.Y., Feb. 19, ’96. The accompanying cut marked “Rice’s Experiment, Fig. [1],” is a diagram representing the several elements of the apparatus, while “Rice’s Experiment, Fig. [2],” shows what kind of a sciagraph can be obtained by means of a Wimshurst machine. [§ 101], at centre. The details of the apparatus as employed by Mr. E. Wilbur Rice, Jr., Technical Director of the General Electric Co., were as follows: A Wimshurst machine, having a glass plate 16 inches diameter, coupled up with the usual small Leyden jars, spark under best conditions of atmosphere, etc., 4 inches. “The usual method of taking pictures with such a machine is to connect the interior coatings of the two jars, respectively, to the positive and negative conductors of the machine, the terminals of the discharge tube being connected between the external coatings of the Leyden jars. In this condition, the disruptive discharge of the Leyden jars passes through the tube and across the balls upon the terminals of the conductors of the machine, the length of spark being regulated by separating the balls in the usual way.” Later, he found that by omitting the Leyden jars, the generation of the X-rays was practically non-intermittent. He therefore connected the terminals of the discharge tube directly to those of the Wimshurst machine as indicated in “Rice’s Experiment, Fig. [1],” which also illustrates the details in the carrying out of the experiment for obtaining the picture, Fig. [2], of the purse containing the coins and a key. The principal feature was the introduction of a lead diaphragm containing a small central opening 7-8 inch diameter opposite the fluorescent spot. Sciagraphs taken thus required a little more time, about 60 minutes, while without the diaphragm, the time could be shortened to about 30 minutes, but the shadows were not so clear in the latter case. The figures are on p. [100].
Rice’s Experiment. Fig. 1, [§ 106], p. [99].
Diagram.
Rice’s Experiment. Fig. 2, [§ 106], p. [99].
Taken with the above apparatus.
107. Source of X-Rays Tested by Propagation Through a Small Hole.—This would illustrate not only that the fluorescent spot is the source of X-rays, but also that a very small portion comes from other parts that are probably bombarded by stray cathode rays (due to irregular surface of cathode [§ 57], or by reflected X-rays or cathode rays.
He tested the source of the X-rays by means of the following arrangement of the apparatus: It will be noticed that the lead diaphragm is quite close to the fluorescent spot. Upon holding the sciascope on the opposite side, and pointing it toward the spot, the luminous area of the fluorescent screen was about the same as that of the opening in the diaphragm, but the size grew rapidly upon receding from the diaphragm. If the rays had come from the cathode, however, the fluorescent spot on the screen would not have increased in size so rapidly during recession, and, therefore, the rays must have come from the spot on the glass struck by the cathode rays. [§ 113], [116], [117].
107a. Leeds’ and Stokes’ Experiment. Use of Stops in Sciagraphy. Western Electrician, Mar. 14, ’96.—In order to obtain clear definitions of the shadows, Messrs. M. E. Leeds and J. B. Stokes provided lead plates with holes, varying in size from 1/4 inch to an inch between the discharge tube on one side and the object and photographic plate on the other. In this manner they obtained excellent sciagraphs of animals having very fine skeletons. See the picture of the rattlesnake at [§ 135] and of a fish on page [63]. See also the frog taken abroad page [90].