PHYSICS, PROGRESS OF, IN 1901. 



535 



cause persistent contact. Zinc and its alloys give 

 the greatest sensitiveness, but nickel and plati- 

 num the most regular results. The degree of oxi- 

 dation has great influence on the sensitiveness. 

 1*. E. Shaw (Philosophical Magazine, March) has 

 added by his experiments to our knowledge of the 

 nature of coherence due to the incidence of elec- 

 tromagnetic waves. Among his conclusions are 

 the following: (1) The insulating layer between 

 the surfaces of the contact is of importance be- 

 fore the first coherence has occurred. (2) In cer- 

 tain cases there actually is a bridge of metal 

 formed between the surfaces and rigidly connect- 

 ed to both. (3) A peculiar molecular change 

 (called orientation) has been brought to light. 

 After coherence has taken place and the current 

 has passed through the coherer in one direction, 

 suppose decoherence to be brought about so that 

 no current now passes; if then the direction of 

 the electromotive force in the coherer circuit be 

 reversed, coherence immediately occurs. 



Electric Waves. G. Pierce (Philosophical Maga- 

 zine, May), with reference to previous measure- 

 ments of refractive indices for electric waves of 

 several doubly refractive media (woods) which 

 were also doubly absorptive, has investigated the 

 question whether the double absorption is suffi- 

 cient to account for the double refraction, and 

 whether both these properties can be ascribed to 

 differences of conductivity along and across the 

 grain. Mathematical analysis shows that in that 

 orientation of electric force in which absorption 

 is greatest, velocity is least, and therefore index 

 of refraction greatest. This agrees with the re- 

 sults of the experiments on woods. In all the 

 specimens tested, both index and absorption were 

 found to be greater when the grain was parallel 

 to the electric displacement than when it was. 

 perpendicular. The author concludes that hetero- 

 geneous conductivity plays an important part in 

 the phenomenon. T. Tommasina (Comptes Ren- 

 dus, Nov. 26, 1900) has used improved carbon 

 coherers as electroradiophones to detect distant 

 thunder-storms. The electrodes are lamp carbons 

 joined to platinum wires and the coherer is sealed 

 to exclude moisture. Three copper antennae, each 

 30 meters long, were fixed to insulators at a 

 height of 12 meters, and one end of each was con- 

 nected to earth. To avoid danger, the antennae 

 were not vertical, and were disconnected and in- 

 sulated on the approach of a thunder-storm. J. 

 D. van der Waals, Jr. (Physikalische Zeitschrift, 

 May 4), seeks to explain radiation phenomena by 

 a statical theory. He applies the probability law 

 to an aggregate of radiating molecules. If in 

 an element of space there is an aggregate of 

 molecules radiating to an external point, P, the 

 electric moments of the molecules are as probably 

 in one direction as in the opposite, but, for radia- 

 tion to reach P, deviations must occur from the 

 most probable distribution of the moments of the 

 molecules; these and the electromagnetic force 

 at P vary as the square root of the number of 

 the molecules. This deduction is based on the 

 assumption that the vibrations are independent 

 of one another, but because of absorption a par- 

 tial arrangement must exist in the molecular vi- 

 brations. The law of this arrangement is yet to 

 be discovered; it involves attractive forces be- 

 tween the molecules, and the author suggests the 

 possibility of thus explaining molecular attrac- 

 tion. 



Electrolytic Phenomena. R. R. Ramsey (Phys- 

 ical Review, July, 1901) has succeeded in meas- 

 uring the very small electromotive force set up 

 between two metallic electrodes at different 

 heights in an electrolytic solution, owing to the 



ilu-ir different 

 two 



difference in weight of tlu ion 



migration velocities. A ml; 



electrodes of zinc or eiulnmii \ 



with zinc or cadmium sulfittc i.-d in 



series with a sensitive galv;niom< ' < *i : n, i;ii-in<i 



the tube from a horizontal to a 



a deflection of the galvanometer . 

 In the case of zinc electrodes in 10 

 sulfate solution the calculated ( I< 

 force was 2.4 X 10~ 8 volts per centirneU < 

 between the electrodes. The mean of tin 

 observations was 3.1 X lO' 8 volts. Similar i. : 

 were obtained with cadmium electrodes in a sc 

 tion of cadmium sulfate. B. D. Steele (.Journal 

 of the Chemical Society, April) has devised a 

 modification of Lodge's method for the measure- 

 ment of ionic velocity in which the velocity is 

 measured directly by means of the movement of 

 the boundary between a colorless and two colored 

 salts in a gelatinized electrolyte during the pas- 

 sage of a current. The author largely avoids the 

 use of gelatin by employing vertical tubes, and 

 finds it possible under certain conditions to observe 

 the boundary between colorless solutions by means 

 of slight differences in density and refractive 

 power, so , that the use of a colored solution is 

 also rendered unnecessary. Riesenfeld (Zeitschrift 

 fur Elektrochemie, May 23) shows theoretically 

 that at the interface between solutions of the same 

 electrolyte in two partially miscible solvents 

 concentration will increase at one junction and 

 decrease at the other (supposing the two solu- 

 tions to be contained in a U-tube), and that this 

 variation will be proportional to the difference 

 between the migration constants of the cation (or 

 anion) in the two solvents. 



Phenomena in Rarefied Gases. W. Kaufmann 

 (German Physical Society) bases an explanation 

 of the negative glow-light and the dark cathode 

 space upon the fact that cathode rays dissociate 

 the gas through which they pass, and render it 

 conducting. As this conductivity disappears 

 rapidly after the discharge ceases, the ions must 

 combine again of themselves, and the author sup- 

 poses that the negative glow-light arises through 

 the impact of ions during this combination. E. 

 Goldstein (ibid.) adheres to his previously ex- 

 pressed views that the glow-light consists of rec- 

 tilinear rays that spring not from the cathode 

 itself, but from the ordinary cathode rays, from 

 all parts and in all directions. Owing to the 

 repulsion exerted by the cathode there is formed 

 around it a space free from glow rays the so- 

 called dark cathode space. Further applications 

 of the principle explain the extension of the dark 

 space when the pressure diminishes; also its re- 

 striction by placing another cathode opposite, or 

 by the action of a magnet. J. Stark (Annalen 

 der Physik, October, 1900) finds that under the 

 influence of heat the luminous layers in a vacu- 

 um discharge show a decrease of potential gra- 

 dient and an increase of current intensity. The 

 changes occur first slowly with increasing tem- 

 perature, then rapidly, and then again slowly. 

 The dark spaces show an opposite behavior. At a 

 red heat the bright layers become dark and ac- 

 quire the properties of the latter. K. Kerkhof 

 (Annalen der Physik, February) has shown that 

 the temperatures of gases in Geissler tubes of dif- 

 ferent diameters are not inversely proportional 

 to the cross-sections, as has been supposed. Prob- 

 ably during the discharge heat is given off to the 

 glass and to the surrounding atmosphere. To test 

 the general opinion tluit the change of the band 

 spectrum to the line spectrum produced by using 

 a spark gap is due to a rise in temperature, the 

 author inserted a spark gap, and found that this 



