PHYSICS, PROGRESS OF, IN 1803. 



623 



to be a fair amount of evidence that the Hull 

 rlTVci i> intimately connected with the action of 

 a magnetic field on light, though further evi- 

 dence is required before it ran lie asserted that 

 lx>th are due to the same ultimate cau~c. He 

 -ts as a desirable line of experiment the 

 i n \ i -t Station of the effect of an electrified con- 

 ductor on light, reflected from it. Kundt (Ber- 

 lin Physical Society, March 10), employing tranc- 

 parent films of iron, nickel, and cobalt, inarnet- 

 i/cd to 'J.s.ooo units, finds that the Hall effect 

 increases with the rotatory power, and therefore 

 with the magnet i/.at ion. K Lommel (Wiede- 

 mann's " Annalen," No. 12,1892) remarks that 

 iron filings on a plate arrange themselves along 

 tho lines of force, which are also equipotential 

 lines, and therefore are at right augles to the 

 lines of flow. If the plate is placed in a mag- 

 netic field these all change position, hence tho 

 Hall effect. 



Discharge in a Gas. J. J. Thomson (" Philo- 

 sophical Magazine," October) remarks that the 

 benaviorof gas to the electric spark is analogous 

 to that of a vapor condensing to liquid, to the 

 freezing of a liquid, or to the deposition of crys- 

 tals from a saturated solution. When a foreign 

 substance, as water vapor, is present the poten- 

 tial difference supportable without discharge is 

 approximately steady, but when the gas is care- 

 fully dried this difference becomes abnormally 

 large. When the discharge once starts it falls 

 to the normal at once, but if the gas is allowed 

 to rest, still remaining dry, it rises again. These 

 phenomena seem to point to the formation dur- 

 ing a discharge of a modified form of the gas, 

 perhaps by condensation of molecules to complex 

 forms, which is hastened by nuclei, just as is tho 

 physical condensation of vapor to liquid. 



Phenomena of Exhausted Tubes and Rarefied 

 Oases. Wiedemann and Ebert (Wiedemann's 

 "Annalen," No. 9), discussing luminous phenom- 

 ena in rarefied gases without electrodes, conclude 

 that these are due to the displacement of tubes 

 of electric force. Any metal plate, they say, in 

 contact with a rarefied gas and exposed to 

 slightly damped electric oscillations snows all 

 the phenomena of a cathode. John Trowbridge 

 ("American Journal of Science," September) con- 

 cludes similarly that the aurora is due not to 

 electric oscillations, but to the redistribution of 

 lines of force produced by suitable earths. Le- 

 nard (Berlin Academy) caused the rays from an 

 aluminum cathode to be projected on an alumi- 

 num window -003 millimetre thick, in a thicker 

 plate. The rays passed through it and made the 

 air faintly luminous with a bluish light, produc- 

 ing also a smell of ozone. Phosphorescent bodies 

 glowed in the path of the transmitted beam as in 

 vacuo. At a distance flf 2'4 inches from the 

 " window " it ceased to act thus, but its penetra- 

 tion varied for different gases. E. Goldstein 

 (Berlin Physical Society, Dec. 16. 1892) finds that 

 the anodic light of silver is brighter than that 

 of aluminum. At the cathode the reverse is 

 true. The effect is only seen in oxygen, and ap- 

 pears due to oxidation of the silver. Rimington 

 and Wythe (London Physical Society, Nov. 25) 

 find that when electrodeless tubes and bulbs are 

 rotated in a constant electric field, a double fan- 

 shaped image results, not symmetrical but dis- 

 placed in the direction of rotation. This is a 



direct transformation of mechanical energy into 

 light. A. A. ('. Swinlon ( Philosophical Maga- 

 y.ine," September) wound a vacuum tube with 

 three turns of copper wire in a course .spiral, one 

 end of which was connected with a high-frequen- 

 cv induction coil, the other being free. In.-idc 



tfie tlllie appeared u blue spiral corresponding to 



the wire, but half a turn in advance of it. This 

 lie accounts for by the repulsion of the residual 

 air within and consequent bombardment of the 

 glass just opposite the wire. E. C. Rimington 

 (London Physical Society, April 28) concludes 

 that the luminous rings observed in exhausted 

 bulbs and tubes when Leyden jars are discharged 

 through coils around them are due rather to 

 rapidly varying magnetic induction than to 

 electrostatic action. When two loops are used 

 so arranged that the electrostat ic effects balance 

 while the magnetic effects re-enforce each other, 

 the luminous phenomena become brighter, while 

 they disappear when the inverse arrangement is 

 adopted. 



Dielectrics. G. Benischke (Vienna " Berichte," 

 April 18) finds that the dielectric constant is in- 

 dependent of the strength of the electric field. 

 He finds the constant to be: For paraffin, 1'89; 

 for ebonite, 2*03 ; for sulphur, 2'42 ; and for glass, 

 4'17 to 4-52, the value for plate glass being 3-85. 

 P. Janet (Paris Academy of Science, Feb. 20), in 

 experiments on dielectric viscosity of mica, by 

 comparison of the differences of potential and 

 resulting charges during rapid oscillation, finds 

 that the charges lag behind the conesponding 

 potential differences analogously to Ewing's 

 curves of magnetic hysteresis. "Charles Borel 

 (ibid., May 23) suspended a disk of paraffined 

 paper by the center before a plate which was 

 charged alternately positively and negatively at 

 intervals of 0-006 second. When an earthed glass 

 rod was held between and on one side, the disk 

 rotated, owing apparently to the mutual action 

 of residual charges. With a conductor or a good 

 insulator there was a feeble rotation in the op- 

 posite direction. 



Condenser. P. Curie (Societe Francaise de 

 Physique) has constructed a very perfect con- 

 denser of two plates of silvered glass separated 

 by three blocks of quartz. The center was sepa- 

 rated from the guard only by a narrow line from 

 which the silver was removed. 



Electrolysis. W. C. Dampicr Whetham (Lon- 

 don Royal Society, Nov. 24) has measured ionic 

 velocities in electrolysis by the motion of the 

 junction between two salt solutions of different 

 density and different color when the current was 

 passed across it. The following are his results, 

 com] tared with values calculated by Kolbaum 

 from the electrolytic conditions of solution, with 

 Hittorf's values of the migration constant : 



