PHYSICS, PROGRESS OP, IN 1892. 



643 



. E. Bouty ("Complex Kendus," 

 Man-h 7) finds that (ho dielectric constant 

 changes but slightly under conditions which 

 vary ill- 1 conductivity greatly, Thus water and 

 toe have xnsiidy the same dielectric constant, 

 whUe the conductivity varie* from 1 to 10* or 10*. 

 Tin liatitt v. H. Abraham ("Uomptes Rcn- 

 diis,".Iune 7) has measured i', the ratio between 

 the electrostatic and electro-magnetic units, 

 by finding tin- capacity of a plane guard-ring 

 condenser in both systems. His result was 



Ct/rrt'iit Measures. Wien (Wiedemann's 

 Amialen," Nov. 12, 1801) uses for this purpose 

 a telephone with a stylus and mirror. The tele- 

 phone diaphragm is attuned to the alternating 

 current to be measured and the stylus touches 

 the mirror, which is fastened to a flexible arm 

 clamped to an adjustable support. The device 

 shows readily 3 x 10" 1 amperes. 



Point Discharges. The British Association 

 committee on this subject report that they have 

 found that disturbing influences which have lit- 

 tle or no effect on the cathode powerfully affect 

 the anode. 



Electricity and Gravity. G. Gore ("Philo- 

 sophical Magazine," September) argues that 

 since the mean E. M. F. of an amalgam or solu- 

 tion and its diluent is always increased by fur- 

 ther dilution, the E. M. P. varies directly as the 

 degree of molecular freedom, and depends on the 

 velocity of the molecule, and hence on the law 

 of gravity. 



The Electric Spark. Toepler (Wiedemnnn's 

 " Amialen," Nos. 7 and 8), with the aid of a Toep- 

 ler- I loltz statical induction machine whose os- 

 cillations were much more rapid than those of a 

 coil, has shown that a spark between a conductor 

 and a water surface is not oscillating. He con- 

 cludes, therefore, that the lightning is probably 

 not oscillatory, and that the production of noise 

 and light does not in general prove the exist- 

 ence of oscillations. 



The Voltaic Arc. Dr. Arons exhibited to the 

 Berlin Physical Society (Oct. 21) an arc light be- 

 t ween mercurial electrodes in a vacuum. A 

 dazzling white light was produced, steady at the 

 anode but flickering and jumping at the cath- 

 ode. The temperature was highest at the cath- 

 ode, but the tube was not at any time too hot 

 to he held in the hand. The current was found 

 by means o/ the telephone to be discontinuous. 

 The spectroscope showed a lime spectrum with 

 brilliant yellow, green, and blue lines. It was 

 attempted to obtain the light also with amal- 

 gams, but without success except in the one 

 instance of sodium amalgam. 



k'/n-trin'ty by Gaseous Friction. Prof. Wes- 

 endruck, of Berlin ("Naturwissenschaft Rund- 

 schau"), finds that dustless air in friction with 

 metals dues not generate electricity, but that 

 can H in diuxide does, and that this is due to the 

 cloud formation that takes place with the latter. 

 Electro-Capillary Phenomena. Gouy (Paris 

 Acj.demy. Jan. 4) has measured the surface ten- 

 sinii of more or less polarized liquid amalgams 

 as compared with mercury. The amalgams test- 

 ed contained IO Vij respectively of zinc, cadmium, 

 1' ail. tin, bismuth, silver, and gold. In a system 

 of nonpolarized mercury, acidulated water, and 

 more or less polarized amalgam the surface ten- 



sion of the amalgam was found to be a function 

 of the apparent difference of potential between 

 the amalgam and the mercurv. 



Magnetism. li-rrestrial Magnetiim. Henrv 

 Wilde has propounded a theory of the earth's 

 magnetism which he illustrates by a remarkable 

 model. According to his view, there have been 

 three stages in the development of terrestrial 

 magnetism: (1) the electro-dynamic stage, where 

 the whole globe, being at a high temperature, 

 was nonmagnetic; (2) the stage where the outer 

 crust had cooled sufficiently to be permanent- 

 ly magnetized, and rotated at a different rate 

 and with different poles from the interior; and 

 (3) the present stage, where the crust magnetism 

 is unsymmetrical, owing to irregiilar configura- 

 tion of land and water. His model reproduces 

 the interior electro-dynamic globe and the outer 

 unsymmetrical, permanently magnetized crust, 

 and by adjusting the inclination of the two 

 axes and the rates of rotation he gets a close 

 imitation of observed phenomena. So close is 

 the correspondence that it has been thought 

 definitely to prove the existence of a liquid in- 

 terior of the earth, and so to settle a vexed ques- 

 tion in geology. But L. A. Bauer (Washington 

 Philosophical Society, Feb. 27) asserts that 

 Wilde's theory involves (1) a secular change 

 every nine hundred and sixty years throughout 

 the entire globe ; (2) the passage through zero of 

 the declination at every point during some time 

 in the cycle; and (3) the approximate equality 

 of the total easterly and westerly declination. 

 These results are all at variance with facts. 

 Bauer therefore concludes, that though Wilde's 

 theory gives a secular variation it does not ex- 

 plain the one that actually exists. E. Marchaud 

 (Paris Academy of Sciences, Jan. 4), by observa- 

 tions made at Lyons Observatory since 1887, has 

 established a connection between lightning dis- 

 charges and disturbances of terrestrial magnet- 

 ism. There were noted 73 discharges, of which 

 40 were accompanied by well-marked disturb- 

 ances of the declination curve. There was no 

 simple relation, however, between the distance 

 of tne discharge and the amplitude of the mag- 

 netic oscillation. William Ellis (" Proceedings of 

 the Royal Society, London," 313) concludes from 

 a comparison of records of magnetic disturb- 

 ances that in the movement preceding a dis- 

 turbance all the magnets at any one place are 

 affected simultaneously, and in places far distant 

 the movement generally occurs at the same time, 

 though there are small differences which may or 

 may not be accidental. 



Propagation of Magnetism in a Metal. Prof. 

 John Trowbridge (" Philosophical Magazine," 

 April) has made further experiments with a view 

 to detecting whether or not this takes place by 

 wave motion, using his phasemeter an arrange- 

 ment by which the vibrations of two telephone 

 diaphragms are compounded and exhibited by 

 means of Lissajous's curves. He finds no true 

 nodes in a bar which is being magnetized, and 

 concludes that, as in the case of heat conduction, 

 magnetization does not proceed in a wave, its 

 propagation being expressed by the equations of 

 motion of molecular magnets in a resisting 

 medium. Julius and Huffel, however, in "Na- 

 ture" (Aug. 'J.">i. assert that the telephone is not 

 a suitable instrument to be used in investiga- 



