554 



PHYSICS, PROGRESS OP, IN 1902. 



two principal directions, corresponding to the 

 mean trend of the crystallographic axes of the 

 metal (bismuth). The mean effect is not the 

 same when an axis of symmetry lies directly be- 

 tween the electrodes and when it does not, owing 

 to the state of aggregation of the bismuth. An- 

 other cause of apparent dissymmetry is the in- 

 crease of resistance along the lines of force. G. 

 Moreau (Journal de Physique, August, 1901) con- 

 cludes from a series of experiments on films of 

 silver and nickel that for films approaching 

 5 X 10-" centimeters thickness the accepted law 

 of the Hall effect does not apply. Apparently 

 the outer layers of a film, to a depth of 2.5 X 10- 8 

 centimeters, have properties differing from those 

 of the interior. Thus the total thickness of a 

 film is the sum of the outer layers together with 

 the thickness of the homogeneous interior. For 

 thin films the usual formula requires amendment 

 so that it may express this fact. 



Rontgen Rays. P. Curie and G. Sagnac (Jour- 

 nal de Physique, January) find that secondary 

 rays, from heavy metals struck by Rontgen rays, 

 carry negative charges and leave positive charges 

 on the metal. In a high vacuum these are inde- 

 pendent of the distance, but in presence of air 

 particles the charges dissociate the neutral elec- 

 tricity of the air into positive and negative parti- 

 cles, resembling in this property the cathode rays 

 and the deviable radiations from radium. Rontgen 

 rays carry no charges, while radium emits un- 

 charged Rontgen rays and charged cathode rays 

 mixed. It is probable that secondary rays pre- 

 sent a similar mixture. R. K. McClung and D. 

 Mclntosh (Philosophical Magazine, January) 

 have compared the absorbing power of different 

 solutions for Rontgen rays by means of two par- 

 allel metal plates at different potentials, between 

 which the rays were allowed to pass. A current 

 is set up between the plates, which will be pro- 

 portional to the intensity of the rays. In this 

 way the relative amounts of rays which pass 

 through different solutions were ascertained. 

 The permeability of a substance was found to 

 be the same for rays of different intensities. An 

 increase in the amount of salt in solution pro- 

 duced an increase in the absorption of the rays, 

 and in general increase of atomic weight causes 

 increase of absorption. E. Villari (Nuovo Ci- 

 mento, August, 1901) finds that when Rontgen- 

 ized air is passed through an insulated zinc tube, 

 and one pole of a dry pile is held near the wall 

 of the tube at its outer end, the tube becomes 

 strongly charged with electricity of the same sign 

 as that of the pole, but there is no charge unless 

 the air is Rontgenized. As the distance between 

 the pole and the end of the tube increases the 

 charge diminishes and practically no charge is 

 perceptible when the distance is 30 centimeters. 

 A screen between the tube outlet and the pole 

 of the dry pile prevents the charging of the tube 

 or ball. This tends to show that the air reaches 

 the pole by diffusion, and communicates its 

 charge to the tube, but this view is contradicted 

 by other facts. (See also Radio- Activity under 

 LIGHT.) 



Hertzian Waves. K. Wildermuth (Annalen 

 der Physik, April 29) has experimented with an 

 oscillator consisting of two spheres immersed in 

 oil, the waves from which passed along a pair 

 of parallel wires, which, in turn, were led through 

 a glass vessel containing a liquid. Thus he has 

 measured the absorption coefficients of compara- 

 tively good and bad conducting liquids. With 

 water, sodium chlorid, and copper-sulfid solu- 

 tions, using waves of a period 21 X 10-', the 

 absorption coefficients are theoretically derivable 



from the conductivities. Waves of a period 

 74 X 10~ u were more strongly absorbed by dis- 

 tilled water than would be expected from its con- 

 ductivity. Lamotte (Journal de Physique, Octo- 

 ber, 1901) has studied electric waves propagated 

 along wires proceeding from one of the ordinary 

 oscillators, with a view to settling the question 

 of whether electric oscillations of higher orders 

 are present under such circumstances. He ob- 

 served waves of different periods, their number 

 being greater as the system is made longer, and 

 among these he reports that he could distinguish 

 two groups whose periods are comparable re- 

 spectively to the period proper to the primary 

 and to that proper to the secondary. In each 

 of the groups the lengths of the waves form a 

 set w r hich tends more and more toward a har- 

 monic series as the length of the vibrating system 

 increases. C. Gutton (Journal de Physique, De- 

 cember, 1901) passed electric waves from a Hertz 

 vibrator along two parallel wires which passed 

 into a tub containing the resonator, and after- 

 ward extended for some distance within a long 

 trough, being connected by a bridge. With first 

 air, then water in tub and trough, the wave- 

 lengths were found to be invariable, with the 

 resonator either in or perpendicular to the plane 

 of the wires. But when the resonator was kept 

 in air and the wires immersed in water the semi- 

 wave-length was reduced from 145 centimeters 

 in air to 17.5 centimeters in water, giving 8.3 as 

 the refractive index of water for the waves. These 

 experiments contradict Turpain's statement that 

 the period of a resonator is independent of the 

 medium in which it is immersed. C. A. Chant 

 (American Journal of Science, January) has at- 

 tempted to discover whether electrical oscil- 

 lators with thin surfaces of metal are as efficient 

 as similar ones made solid or with thicker 

 skins. Oscillators of the cylindrical and of 

 the spherical type were used, made of solid 

 brass, solid Norway iron, copper tubing, solid 

 electric-light carbon, sheet platinum on a wooden 

 form, sheet silver, tinfoil on wood, gold-leaf on 

 wood, silver-leaf on wood, copper deposited elec- 

 trolytically, and silver deposited chemically on 

 glass. The results show that, in the case of the 

 cylindrical and spherical doublets, the various 

 thin mantles, and even the excessively thin gold- 

 leaf shells were as efficient as the 'solid meti " 

 bodies. 



ColH-rcncr.W. H. Eccles (Electrician, Aug. 

 23-30, 1901) finds, from various experiments, in 

 opposition to the views held by several authorities, 

 that electrical surgings, such as are produced in 

 any circuit to which an electromotive force is 

 abruptly applied, have no effect in producing co- 

 herence. Tlie phenomenon, as Branly and others 

 have maintained, is an effect of electromotive force 

 merely. Coherence is a continuous phenomenon, 

 and there can be no true " critical voltage." The 

 author makes the typical coherer consist of filings 

 free to move throughout the space of a narrow 

 crevice, bounded at its ends by plane conducting 

 surfaces. E. Branly (Comptes Rendus, May 26) 

 has devised a coherer consisting of a steel disk 

 with three legs ending in blunt oxidized points 

 resting upon a polished steel disk. Decoherence 

 is effected by a very slight tap, and there is a 

 corresponding increase in speed. The author 

 finds this form very regular and reliable in ac- 

 tion, and that it will continue in working order 

 for several months. When transmitting a mes- 

 sage, the tripod of the coherer at the sending sta- 

 tion is slightly raised from the lower disk by 

 means of an auxiliary electromagnet, which pre- 

 vents it from being 'effected by the transmitter 





