692 



RONTGEN RAYS. 



use of lenses was not possible, for the rays were not 

 refrangible, so that in all cases the object to be 

 photographed was necessarily held as close as pos- 

 sible to the sensitive plate, and the resulting picture 

 was exactly of the same size as the original. To 

 this application of the new discovery it undoubtedly 

 owed the extraordinary and widespread interest. 

 that it at once aroused throughout the civilized 

 world. Important as it wns as a link in the long 

 chain of experiments on cathode phenomena that 

 had been diligently prosecuted for years, especially 

 in Germany and England, this purely scientific 

 interest was completely overshadowed in the pub- 

 lic mind by the sensational features of the an- 

 nouncement that a means of "seeing through " the 

 human body had been devised. Misstateinents and 

 exaggerations were inevitable, but experimenters 

 in all countries at once verified Prof. Rontgen's 

 own announcement. His statement still remains 

 accurate, except that the rays have been found 

 capable of reflection in a very slight degree. They 

 are incapable of polarization (Mayer, "Science," 

 March 27), discharge electrified bodies, and electrify 

 neutral bodies (Righi, " Comptes Rendus," Feb. 17), 

 some positively and others negatively (Minchin, 

 "Electrician," London, March 27). Negative 

 charges are dissipated faster than positive, the rate 

 depending on absorption (IVnnist and llermuzescu, 

 "Comptes Rendus," Feb. 3, March 17, and April 

 27). Many more substances are opalescent to X 

 rays than to light, owing to internal diffusion 

 (Pupin, "Science," April 10; Thomson, "Electrical 

 World," April 25), hence the shadow pictures taken 

 with the rays are never absolutely clear cut. 



The precise source of the rays was at first a sub- 

 ject of some controversy. "ROntgen, as stated 

 above, announced that they arise from the part of 

 of the glass wall of the vacuum tube on which the 

 cathode rays impinge. Elihu Thomson showed 

 that the rays did not proceed directly from the 

 anode or the cathode. Rice ('' Electrical Engineer- 

 ing," April 22) confirmed the opinion of Rontgen, 

 and others have been able to show that they arise 

 at a spot directly opposite the cathode. When the 

 cathode is in the center of the tube (" Electrical 

 W'orld," March 14) there are two such spots. 

 Stine (ibid., April 11) obtained similar results, and 

 also showed that effects that might be supposed to 

 indicate diffraction of the rays were really due to 

 penurabral shadows. Scribner and M'Berty (" Elec- 

 trical Engineering," April 8) proved that the source 

 of the rays was on the inner surface of the glass. 

 On the other hand, De Heen (" Comptes Rendus," 

 Feb. 17) believed the anode to be the source of the 

 rays, but possibly the anode in his experiment was 

 struck by the cathode rays. Lodge (" Electrician," 

 April 10) showed that it emits the rays powerfully 

 when so struck, and he concluded that X rays 

 "start from a surface on which the cathode rays 

 strike, whether it be an actual anode or only an 

 anticathodic surface." In the cases first observed the 

 glass was such a surface. Lodge believes that the 

 glass emits X rays just as a red-hot surface emits 

 light, each point radiating them independently of 

 the others, and he showed that glass that became 

 " fatigued " in its power to emit luminous phospho- 

 rescence did not become fatigued in emission of X 

 rays, these remaining of the same power, while the 

 phosphorescent spot from which they proceeded grew 

 dimmer. Rowland ("Electricity," April 22) be- 

 lieves that the spot from which the rays arise on 

 the glass is " an induced anode," and that the neces- 

 sary condition for the production of X rays is the 

 bombardment of an anode by the cathode discharge. 

 Salvioni and others found that the phosphorescent 

 spot could be shifted by a conductor brought near 

 it outside. Roiti (" Atti dei Lincei," July) finds 



that cathode rays do not give rise to X rays when 

 they impinge on gases. Piltchikoff ("Comptes 

 Kendus," Feb. 24) showed that a tube containing an 

 easily Jluorescent substance emits a larger quantity 

 of X rays than the common tube. Edison showed 

 that the penetrating power of the rays is increased 

 by reduction of temperature. Tesla succeeded in 

 obtaining evidence of the rays at a distance of 60 

 feet from the source. 



The question of reflection was taken up by sev- 

 eral experimenters, and it soon appeared that the 

 rays could be reflected, although very slightly. 

 Rood (" Science," March 27) concluded that (he per- 

 centage of reflected rays was about O'OOS. The re- 

 flection was generally thought to be irregular or dif- 

 fusive, but Mayer (ibid.. May 8) is of opinion that 

 there is a slight regular or specular reflection. 

 Tesla arranged a device by which sciagraphs were 

 taken with reflected as well as transmitted rays, 

 and the results were compared. This shows rough- 

 ly that the best reflectors of the rays are zinc, lead, 

 tin, and mica, which reflect about 3 per cent, of the 

 incident rays. 



From the fact that the rays discharge both 

 negatively and positively charged bodies, as stated 

 above, it was inferred by some that the conductiv- 

 ity of the bodies is increased by X rays. Tesla, 

 however ("Electrical Review," June 24), believes 

 that he has proved the contrary. Murray (London 

 Royal Society, 31 arch 19) showed that the rays 

 lower the contact potential of metals. 



From the first it was surmised that the rays 

 might have some peculiar effect on living bodies, 

 but none has been directly proved. Exposure to 

 t he rays in certain instances has, it is true, resulted 

 in the loss of hair and in painful symptoms re- 

 sembling those of powerful sunburn, but it is be- 

 lieved by many that these are due not to the X 

 rays, but to ultra-violet light that accompanies 



FlO. 4. TYPICAL FOCUS TUBE. 



them. Tesla reports an anaesthetic effect, but it has 

 been noticed by no one else. Experiments to de- 

 termine their action on micro-organisms have been 

 conflicting, and in most cases negative. 



No mechanical action of the rays similar to that 

 exerted by the cathode rays within the tube has 

 been noticed, although experimenters have looked 

 for it. Gossart ("Comptes Rendus," Feb. 10) 

 thought that the radiations caused radiometer vanes 

 to cease their rotation, but the action was shown 

 later by Fontana (ibid., April 13) to be electro- 

 static. Porter (" Nature," June 18) found the radi- 

 ometer entirely inert to Rontgen rays. 



Diligent search has also been made for X rays in 

 other radiations, but they have been obtained no- 

 where except from discharge tubes, reports to the 

 contrary being generally discredited by scientific 

 men. Special efforts have been made to discover 

 the rays in sunlight, but with negative results. 



Applications and Apparatus. Applications of 

 the Rontgen rays in science and the arts have so 

 far depended entirely on their property of passing 

 through objects that are opaque to ordinary light, 

 together with the fact that different substances in- 



