PHYSICS, PROGRESS OF, IN 1898. 



086 



though they can not be used photographically be- 

 cause a brush discharge passes from tube to sensi- 

 tive plate. The distinction between anode and 

 cathode rays disappears. Wehnelt (Wiedemann's 

 "Annalen," July) finds that the resistance of the 

 dark cathode space to electric discharge is consid- 

 erable, giving to the latter a disruptive character 

 as if it were filled with a dielectric. E. Wiede- 

 inaini (Wiedemann's " Annalen," jubilee volume) 

 finds that when a positive-wire anode is brought 

 into the dark cathode space the resistance of the 

 intervening gas is increased, the positive light 

 bending back till it merges in the negative glow. 

 The same result follows the surrounding of the 

 anode with a narrow tube. Gill (" American Jour- 

 iiiil of Science," June) explains the stratification of 

 tlio vacuum tube as a form of Kundt's experiment 

 in which heaps of powder accumulate at the nodes 

 of a vibrating air column, the heaps being repre- 

 sented by strata of molecules between which the' 

 discharge is taking place in a luminous form (see 

 also above, under Discharge). Swinton (London 

 Physical Society, March 25) has investigated the 

 circulation of gaseous matter in a Crookes tube, 

 using a mica mill on a sliding rod, and finds that 

 at high exhaustion a positively charged anode 

 stream moves outside the cathode stream and in 

 an opposite direction. At very high vacua there 

 may be a regular circulation of positive and nega- 

 tive atoms. Birkeland (Paris Academy of Sciences, 

 Feb. 21) finds that the discharge in a Crookes tube 

 is uninfluenced by a magnet beyond a certain dis- 

 tance, but that, as it approaches, there is a critical 

 position at which all the properties of the discharge 

 are suddenly changed, the difference of potential 

 between anode and cathode being reduced to one 

 tenth, and the cathode rays being succeeded by 

 others that produce no phosphorescence. This 

 critical distance increases with the strength of the 

 magnetic field. Kaufmann and Aschkinass (Wie- 

 demann's " Annalen," December, 1897) find that the 

 amount of deflection of cathode rays produced by a 

 narrow field due to condenser plates mounted in a 

 tube that crosses the vacuum tube at right angles 

 is in accordance with the projection rather than the 

 wave hypothesis. Paalzow and Neesen (Wiede- 

 mann's " Annalen," jubilee volume) find that when 

 the force lines of a magnetic field lie across the 

 path of a vacuum discharge the current is always 

 enfeebled and sometimes broken. Villard (Paris 

 Academy of Sciences." July 25), in a study of the 

 phenomena supposed by S. P. Thompson to be 

 caused by what he calls " paracathodic rays," at- 

 tributes them to the diffusion of ordinary cathode 

 rays. The same investigator (" Bulletin " of the 

 Societe Franchise de Physique, Nos. 108, 111) sug- 

 gests that the cathode rays, from their reducing 

 action, may consist wholly of hydrogen atoms due 

 to traces of moisture in the vacuum tube. Wiede- 

 mann and Wehnelt (Wiedemann's " Annalen," 

 March) find that when the lines of force are paral- 

 lel to the axis of the tube the cathode rays are 

 twisted into a bundle with successive nodes. This 

 agrees with the theory that supposes the rays to 

 consist of projected particles. Capstick (London 

 Royal Society, May 26) has measured the fall of 

 potential in the immediate neighborhood of the 

 cathode in vacuum tubes, which is constant for 

 the same gas, and which, he thinks, will prove 

 to be connected with other constants. The values 

 in volts for the gases experimented upon were 

 as follow : 



Witter vapor ItV.t 



Ammonia 582 



Nitric oxide 373 



Nitrogen 232 



Oxygen 369 



If gaseous conduction is electrolytic, the author 

 thinks these numbers may be proportional to the 



heats of dissociation, and thus the experiments 

 might be taken to support Prof. J. J. Thomson's 

 view that the current is carried by particles smaller 

 than atoms, the result of their disintegration. Wien 

 (Wiedemann's "Annalen,'' June) calculates that the 

 velocity of the cathode rays is one third that of 

 light. Malagoli and Bonacini (" Atti dei Lincei," 

 VII, IV) find that both electrodes emit what they 

 call " orthocathodic rays" at the same time, but 

 that which connects with the negative pole of the 

 exciter develops them more intensely. From the 

 electrodes at a certain stage f rarefaction start 

 two oppositely charged cones of radiation, one 

 inclosed in the other or partially separate. The 

 violet anodic light, like the orthocathodic rays, 

 is intensely affected by a magnetic field, but oppo- 

 sitely. Goldstein (Wiedemann's "Annalen," Janu- 

 ary) finds that when the cathode is perforated the 

 yellow layer next it streams through in rays called 

 by him " canal rays," and fill the tube on the anode 

 side, prolonging the cathode rays backward. They 

 are not deflected by a magnet and produce no 

 phosphorescence. (See also the next paragraph.) 



Rontgen Rays (see RO"NTGEN RAYS, in "Annual 

 Cyclopaedia " for 1896). Crookes, in his presidential 

 address before the British Association (" Nature." 

 Sept. 8), states asanow generally accepted conclusion 

 that collisions among the flying atoms of an atten- 

 uated gas or their impact on an object in their path 

 give rise to Rontgen radiation. " It has," he says 

 " for some time been known that whereas a charged 

 body in motion constitutes an electric current, the 

 sudden stoppage or any violent acceleration of such 

 a body must cause an alternating electric disturb- 

 ance, which though so rapidly decaying in intensity 

 as to be practically ' dead beat,' yet must give rise 

 to an ethereal wave or pulse traveling with the speed 

 of light. If the target on to which the electrically- 

 charged atoms impinge is so constituted that some of 

 its minute parts can thereby be set into rhythmical 

 vibration, the energy thus absorbed reappears in the 

 form of light, and the body is said to phospho- 

 resce." Stokes similarly holds that the rays are due 

 to the disturbed electric field caused by the sudden 

 stoppage of the electrically charged atoms that con- 

 stitute the cathode rays an explanation already 

 advanced by him to account for the Lenard rays 

 before the discovery of those of ROntgen. This 

 theory, now named the ' pulse " theory, has an im- 

 portant bearing on the whole theory of light. Ac- 

 cording to it the disturbance that causes the X-ray 

 phenomena is transverse, but of very short wave 

 length. J. J. Thomson (" Nature,'' May 5) also be- 

 lieves the rays to be " pulses " rather than short 

 waves, " not," he says, " because I think the proper- 

 ties of the latter would be different from those of 

 Rontgen rays so far as we know them, but because 

 electro-magnetic theory shows that pulses and not 

 waves are produced by the impulse of cathode 

 rays." Trowbridge. summing up his experiments 

 in " The Century Magazine," concludes that the 

 rays include two classes of phenomena an elect ri- 

 cal disturbance and its conversion into fluorescent 

 light. His experiments show that anode rays as 

 well as cathode rays exist and that both are subject 

 to the laws of electrical induction. We should not 

 expect, therefore, he thinks, that the rays should be 

 reflected or refracted like light. Rontgen. the dis- 

 coverer of the rays (Berlin Academy of Sciences), 

 concludes that they consist of a mixture of rays of 

 different absorbability and intensity, that ray* which 

 produce equal fluorescence can be photographically 

 different, and that the eye is not entirely passive to 

 the rays. Campbell-Sw'inton (London Royal Soci- 

 ety, June 16) has studied the active area on the 

 anti-cathode of a focus tube by means of pin-hole 

 photography, and finds among other things (1) that 



