ATMOSPHERIC AND OTHER ELECTRICITY 121 



The cathode rays possess pecuhar interest in relation to ether, electricity, light, phosphorescence, &c. The term 

 catlwde, which was introduced into electrical nomenclature by Faraday, is derived from the Greek Kara (down), 

 and oSoi (a way), and originated in the early belief that electricity flowed in a downward direction from the 

 positive to the negative pole. The term is apphed to the negative terminal of a battery or of a RuhmkorfE 

 coil or transformer. The counter term anode is apphed to the positive terminal. If the wires connecting the 

 cathode and anode of a Ruhmkorff coil be imbedded in a small glass vessel, and the air in the vessel exhausted, it 

 is found that when the coil is excited, and a high state of exhaustion reached, the cathode rays stream from the 

 cathode in straight lines, and the vessel is filled with luminosity. There is apparently no connection between the 

 cathode and anode, the rays from the cathode not seeking the anode. This seems proved by placing the cathode 

 and anode above each other at the end of an exhausted tube. In such circumstances, the cathode rays hold on in 

 straight lines to the opposite end of the tube, and do not bend round to the anode. It is not quite certain whether 

 the luminosity produced is wholly electrical, or, as Sir William Crookes suggests, partly due to the impact of molecules 

 of the gas on phosphorescent substances which emit light, which results in bombardments of the electrodes on the 

 walls of the containing vessel. In the extraordinary light efEects produced by currents of high frequency " we have 

 to do with an increased activity of the molecules of a rarefied gas, which is produced by the electrical energy stored 

 up in the medium near the electrodes. The cathode rays may be considered as a radiation of electric energy, 

 which is made visible in rarefied media, and which can also be detected outside such media. The visible trans- 

 formation of electric energy from the electrode, termed the cathode, can be made to pass through metal walls, and 

 can be seen outside those metal walls. The cathode rays can be made to pass through substances which are 

 entirely opaque to ordinary hght. Thus, they can be made to pass through sheets of aluminium, gold, silver, and 

 many other opaque materials which entirely cut ofE ordinary light. The cathode rays spread in all directions. They 

 excite phosphorescent bodies, such as uranium glass, to a brilliant glow, and blacken photographic plates. No 

 heating effect of the cathode rays has been detected." ^ 



According to Lenard, ether is the medium by which the cathode rays travel and in which they manifest their 

 peculiar phenomena. This follows, because in tubes where the exhaustion is pushed to an extreme, and where 

 the vacuimi is nearly perfect, the cathode rays cannot be produced, and all electrical manifestations visible as 

 light disappear. 



Scarcely less interesting than the cathode rays are the Rontgen or X-rays discovered by Professor Rontgen. 

 These rays will pass through several inches of wood and thin layers of aluminium. They are, however, almost entirely 

 intercepted or cut off by layers of glass or silver. 



Rontgen, by the aid of the X-rays and by employing ordinary dry plates, has been able to take photographs 

 through wood and the soft tissues of the body ; the rays, because of specific absorbing powers, distinguishing between 

 the soft and hard parts and reveahng the skeleton. He is of opinion that the X-rays are excited either in the glass 

 walls of a Crookes tube, or in the media outside the tube by means of the cathode rays. 



The Rontgen rays are rendering immense service to surgery, as they enable the surgeon to photograph not only 

 the bones of the body, but also foreign opaque substances, such as bullets, needles, pins, portions of glass, &c., 

 accidentally lodged in the soft tissues. Already the bones of the arms and hands, the legs and feet, the chest, pelvis, 

 and backbone have been photographed. Even the heart has been shadowed forth, and some are sanguine enough 

 to beheve that by and by the whole internal economy of the hving body will be revealed by Rontgen ray and 

 similar photographic processes. The late Professor Sir J. Y. Simpson, of Edinburgh, expressed his confident behef 

 that the day would come when the whole hving human body would, by means of electrical or other hght, be rendered 

 diaphanous or transparent, and so exposed to the gaze of the anatomist, physiologist, physician, and surgeon. 

 This would be a notable advance in another, though not wholly different, direction. 



The Rontgen rays pass more readily through the flesh than through the bones and denser parts, and the hope 

 is entertained that the rays may ultimately be made to discriminate between the softer and harder tissues, and provide 

 graduated photographs. 



It is difficult to say whether the Rontgen rays are due to radiant matter streaming from the negative pole 

 (cathode) or to longitudinal waves of electricity. 



According to Maxwell's electro -magnetic theory of hght, only transverse waves are set up in the ether ; longi- 

 tudinal waves being absent. According to the electro-magnetic theory of Helmholtz, both transverse and longi- 

 tudinal waves are present. The Rontgen rays are probably identical with the longitudinal rays postulated by 

 Helmholtz, and which travel with incredible velocity. Rontgen himself inclines to the longitudinal wave theory. 

 D. A. Goldhammer ^ supports the hypothesis that the X-rays are ordinary transverse vibrations of the ether analogous 



1 Trowbridge, op. cit. pp. 281, 282, 283. 



2 Annalen der Physik und Ckemie, No. 4, 1896, 



VOL. I. 



