

PHYSICS, PROGRESS OP, IN 1902. 



555 





sparks. D. Mclntosh and J. Graham-Willmore 

 (Electrical World and Engineer, May 31) de- 

 scribe a series of experiments made to investigate 

 a coherer effect described by A. F. Collins, as oc- 

 curring in fresh brain substance. They report 

 they were unable to obtain any evidence to show 

 that such an effect existed. Trials were made 

 with the brains of animals before and after death, 

 and with a human brain quickly removed from 

 a recently dead person. Tommasina (Physical 

 and Natural History Society of Geneva, April 4, 

 1901) opposes Bose's theory that coherence is due 

 to molecular distortion. He has succeeded in 

 forming visible chains of particles suspended in pe- 

 troleum between two electrodes. The dielectric 

 particles formed chains first, and as the field in- 

 creased in strength the metallic particles followed, 

 "being finally welded by minute sparks. Spontane- 

 ous decoherence is due, according to the author, 

 to the interposition of non-conducting particles 

 between the conducting particles. 



Vacuum-Tube Phenomena. H. Pellat (Comptes 

 Rendus, Dec. 23, 1901) finds that when a long 

 tube is laid through a magnetic field, at right 

 angles to it, and the field is set up, not only is the 

 anode light driven toward the strongest part of 

 the field, but the stratifications seem to collect 

 into the same region, and also become inclined 

 to the axis of the tube. This crowding and slant- 

 ing occurs in uniform or non-uniform, constant or 

 variable fields, and best with fields of from 90 to 

 170 c.g.s.' units. If the tube be put through the 

 holes in pole-pieces made use of in rotary polariza- 

 tion, when there is no field the tube is between 

 the pole-pieces filled with the anode light; but 

 with a field of from 2,500 to 3,000 c.g.s. units the 

 light shrinks to about one-third, and remains ax- 

 ial. The fact that the field is about 3 per cent, 

 stronger along the axis between the holes than 

 opposite the margins would explain a concentra- 

 tion of magnetic oxygen molecules along the axis 

 of the tube, but would not explain the similar be- 

 havior of diamagnetic hydrogen. Possibly hydro- 

 gen may become magnetic in a Geissler tube. The 

 same investigator in a later paper (ibid., May 

 5) reports that when the part of a Geissler tube 

 which is well illuminated by anode rays is placed 

 so that the lines of a magnetic field are perpendic- 

 ular to the rays, fields up to 425 c.g.s. units devi- 

 ate the column and form on the wall of the tube 

 a luminous strip which becomes thinner and more 

 intense as the field becomes stronger. But for 

 higher field strengths the luminous strip increases, 

 and for strengths of 7,000 to 8,000 units the anode 

 column once more fills the whole section of the 

 tube almost uniformly. The resistance of the 

 tube then becomes enormous. But if the lines of 

 force be in the same direction as the anode rays, 

 there is no such increase of resistance. Thus the 

 anode stream, like the cathode stream, experiences 

 a very large mechanical resistance perpendicular 

 to the lines of force of an intense magnetic field, 

 while the resistance to its progress in the direc- 

 tion of these lines of force is feeble. In the latter 

 case, with the ends of the tube inserted into holes 

 in the pole-pieces, the anode column becomes nar- 

 rowed into a thin cylinder occupying only the 

 axis of the tube, which is explained by the result 

 noted above. J. B. B. Burke (Philosophical Mag- 

 azine, 1, 342 and 455, 1901) finds that between 

 certain limits of pressure, which vary for different 

 gases, a brilliant phosphorescence follows the pas- 

 sage of the ring discharge in an electrodeless 

 vacuum-tube, and lasts sometimes for one or two 

 minutes. The author believes this glow to con- 

 sist " of glowing particles or molecules which do 

 not carry an electrical charge, which are not de- 



stroyed or broken up by an electromotive force 

 sufficiently small not to produce a discharge in 

 the gas, and which are not created by the recom- 

 bination of ions along the tube, but are particles 

 or molecules that are produced in the bulb by the 

 passage of the ring discharge and make their way 

 down quite independently of the electrical condi- 

 tion of the tube." The presence of oxygen seems 

 a necessary, though not a sufficient, condition for 

 the glow. The phosphorescent particles " appear 

 to consist of large molecular groups formed by 

 the spark, and which may continue in existence 

 for some time (notwithstanding the bombardment 

 from the molecules of the gas) in consequence of 

 the repulsion which they must exert on mole- 

 cules that approach them." C. A. Skinner (Phil- 

 osophical Magazine, 2, December, 1901) believes 

 that he has demonstrated by experiment that the 

 high potential required to produce a discharge be- 

 tween electrodes in a vacuum-tube is due to a 

 drop of potential between metal and gas. He has 

 examined the conditions controlling this drop, 

 and finds that as the anode is moved toward the 

 cathode, the drop at the anode remains constant 

 along the positive column, while within the Fara- 

 day dark space it first increases to a certain max- 

 imum value, and then falls rapidly to a value 

 approximately zero in the negative glow. It re- 

 mains at zero through the negative glow, but in- 

 creases rapidly on entering the cathode dark 

 space. From investigation of the effect of the 

 area of the cathode on the drop at that electrode, 

 the conclusion is drawn that the cathode drop 

 may be designated as a linear function of the cur- 

 rent density. O. Lehmann (Annalen der Physik, 

 December, 1901) describes experiments to ascer- 

 tain what alterations take place in electrical dis- 

 charges through rarefied gases when they take 

 place in spacious receptacles instead of the usual 

 narrow tubes. In two large bell-shaped air-pump 

 receivers cemented together the normal form 

 is the glow discharge, characterized by the ab- 

 sence of the so-called positive column of light. 

 The cathode is surrounded by three strata, of 

 which the first is a seam of yellow light, while 

 about the anode is a film of pinkish positive gl nv- 

 light. At a suitable air-pressure not more 

 than 360 volts suffice for the discharge, and the 

 dark space is more than 39 centimeters thick. 

 Provided the air-pressure remains unaltered, the 

 thickness of the dark space of the cathode sec- 

 tion decreases when the electromotive force and 

 currents are increased, and vice versa. When 

 the current comes from a condenser of large ca- 

 pacity, and the conducting wires are of low re- 

 sistance, the discharge at a low voltage appears 

 to be continuous, while, on increasing the voltage, 

 sparks fill the whole receptacle with blinding 

 white light. Even at a voltage so low that the 

 discharge does not occur spontaneously, a mag- 

 netic field of proper strength, in a suitable posi- 

 tion, produces brilliant discharges accompanied 

 by a loud crackling noise. The author asserts 

 that the material so far collected will not explain 

 these phenomena. Either of the following three 

 theories may be the true one: (1) The older 

 theory that discharge consists essentially in a 

 sudde'n disappearance of the dielectric condition of 

 polarization, while positive and negative dis- 

 charges alternate in quick succession. (2) A 

 theory corresponding to the newer electron hypoth- 

 esis, according to which this process represents a 

 combination of two or more open currents of 

 different kinds, which appear simultaneously, 

 and by combination form a closed current. (3) 

 Radiancy is merely an accompanying phenome- 

 non, while the current itself passes continually, 



