KAYS. 



693 



tercept them in different decree.- and with their 

 properly \ affecting ;t photographic plate like 

 li<, r ht and of causing certain salts to fluoresce bril- 

 liantly. To olitain a pennaiieiit shadow picture by 

 their means the same method as that used by the 

 discoverer is -till employed, although it has been 

 what perfected. The object to be examined 

 is placed as < ilile to a >ensitive plate, 



covered to shut out 

 ordinary light, and - 

 both are exposed to 

 a discharge tube. 

 The "focus tube" 

 used by Kontgen in 

 his later experi- 

 ments, and also at 

 King's College, 

 London, is shown 

 in the illustration 

 (iMg. 4). The ca- 

 thode (K^ is con- 

 cave and the anode 

 (A) is formed of 

 platinum and is 

 plain. The anode 

 is inclined at such 

 an angle that the 

 X rays generated 

 on its surface by 

 impact of the ca- 

 thode rays are 

 thrown out through 

 the side walls of 



the bulb. The X rays emanate nearly from a 

 point and the shadow pictures are therefore clearer. 

 The apparatus employed by Shallenberger (''Elec- 

 trical World." March ?) is shown in another illus- 

 tration (Fig. 5). A later tube, first proposed by 

 Elihu Thomson, with double anode and two cath- 

 odes, is also shown (Fig. 6). Tesla also used a 

 tube with a single internal electrode. The tube 

 was of very thick glass except just opposite the 

 electrode, which was an aluminium disk having 

 nearly the diameter of the tube. An electric screen 

 was provided, consisting of bronze paint applied 

 to the glass between the electrode and the neck. 

 This form of tube produced the same effect on 

 a sensitive plate in about one quarter the time re- 

 quired by a spherical one. He also immersed 

 his tube in oil to overcome difficulties connected 

 with sparking and with breaking of the tube. To 

 excite his tube Rontgen and his immediate fol- 

 lowers used the induction coil. The Holtz and 

 Wimshurst machines were probably first used in- 

 dependently by Prof. Pupin and I)'r. Morton, both 

 of Xew York' (" Electricity." Feb. 1!M. In the 

 apparatus used by E. W. Rice ("Electrical En- 

 gineering." April 22) the cathode is flat and the 

 source of the X rays is the opposite glass, in front 

 of which a pierced lead diaphragm is used as a 

 "stop." Successful operators have employed ap- 

 paratus of the following description and dimen- 

 sions: Edison used the usual incandescent lamp 

 continuous current at 110 to 120 volts, and a coil 

 having an interrupter operated by an electric mo- 

 tor and making 400 interruptions a second. Pupin 

 ("Science," April 10) finds a powerful coil indis- 

 pensable, and regards the ordinary vibrating inter- 

 rupter as too slow. He uses a rotary one. operated 

 by an electric motor and giving 60 breaks a sec- 

 ond. Tesla ("Electrical Review." March 11 and 

 18, April 1 and 8) has obtained noteworthy re- 

 sults by using his well-known system for producing 

 high potential and frequency, the primary gen- 

 erator being either for direct or alternating cur- 

 rents. Shallenberger ("Electrical World." March 

 17) employed the Tesla system, the current being 



taken from an alternator of a frequency of ]::. 

 second and passed through the primary coii 

 transformer for raising the voltage from ] 



Ki.lMKI or even _>.">. (MM I. Tin- -< eondary CU)T> I ; 



then passed through condensers and a doubl- 

 cade of brass cyhiiii. g thus changed into 



an oscillatory nigh-frequency current, it was then 

 1 through a second coil, and thus a current of 



EMiKRGER S AHPARATfS FOR THE I'ROI) 



V;.")0.(i00 volts was obtained, which was used to ener- 

 gize the discharged tubes. The time of exposure 

 is dependent upon the distance from the source. 

 Edison states that "roughly the duration of ex- 

 posure may be reckoned as proportional to the square 

 of the distance." Frost ("Science." March 27) 

 found that the inost rapid plate for light did not 

 give the deepest image for X rays, and that the 

 mean rapid plate is preferable. Georges Meslins 

 mptes Rendus." March 23-30) reduced the 

 time of exposure by magnetically deflecting the 

 cathode rays, thus condensing the active fluores- 

 cent spot on the tube and increasing the intensity 

 of the rays. The time may be lessened by the use 

 of fluorescent salts on the sensitive film, which 

 Salvioni in Italy. Swinton in England, and Pupin 

 in this country were among the first to use. Swin- 



' ,- l\v \\ 



I \\ v . \ ' \ 

 I'lli. 0. X-RAY TUBE WTTH TWO CATHODES AND DOfBLE ANODE. 



ton was able in this way to obtain a sciagraph of 

 the bones in less than ten seconds, whereas without 

 the fluorescent material two minutes were required. 

 The salt used was calcic tungstate. Henry and 

 others preferred phosphor-sulphide of zinc : others 

 used barium platinocyanide ; and Gifford ("Na- 

 ture," May 21). after a series of experiments with 



