658 



PHYSICS, PROGRESS OP, IN 1894. 



(Wiedemann's " Annalen," September) obtain re- 

 sults that contradict Mnscart and Joubert's as- 

 sumption that small dielectric bodies in an elec- 

 trostatic field do not exert forces on each other. 

 They find that bars and plah's so situated tend 

 to turn with axes or planes parallel to the lines 

 of force. A small disk of sulphur or paraffin 

 hung between condenser plates may thus serve 

 as a "dielectric voltmeter." Nicolaieff (Paris 

 Academy of Science, Sept, 3) has studied dis- 

 placement currenls in dielectrics by suspending 

 disks or rings of dielectrics between the poles of 

 an electro-magnet and observing the differences 

 of displacement for constant and alternating 

 currents due to the secondary field set up by 

 displacement currents in the latter case. Elec- 

 trolytes in annular glass tubes were found to be- 

 have just like perfect dielectrics. 



Sperilif Inductive Capacity. 0. B. Thwing 

 (" Physical Review," July-August), by using an 

 electric resonance method of great simplicity, 

 has obtained the specific inductive capacity of a 

 large number of dielectrics, and has attempted 

 to establish a relation between these and their 

 chemical constitution. Blondlot (Paris Academy 

 of Science. Oct. 8) finds, by measuring the propa- 

 gation of electro-magnetic waves in ice, that its 

 specific inductive capacity is 2'04. Bouty had 

 previously obtained by other methods the value 

 78 a capacity enormously greater than that of 

 any other dielectric. Robert Weber ("Archives 

 de Geneve, xxix, 571) finds that for air and for 

 carbon dioxide the inductive capacity diminishes 

 with the electro-motive force of the charge, and 

 that for ether it increases with the difference of 

 potential. Conducting bodies have an inductive 

 capacity that remains finite. No relation exists 

 between the composition of a mixture and its 

 specific inductive capacity. The absolute values 



do not follow Maxwell's law (\/k = ri). 



The Voltaic Arc. Violle ("Journal de Phy- 

 sique," December) regards the voltaic arc as the 

 seat of a definite physical phenomenon the 

 ebullition of carbon since it is characterized 

 by all the circumstances of normal ebullition. 

 Moissan. however, from microscopical examina- 

 tion of minute fragments of pure carbon, part 

 of which had been electrically vaporized, con- 

 cludes that there is no trace at all of fusion. 

 With impure carbon a chemical compound, as a 

 boride or silicide, may be formed which will 

 fuse. Mascart (Paris Academy of Science, Oct. 

 29) finds that metallic vapors accumulate at the 

 negative pole of the arc, and cyanogen and 

 acetylene at the positive an effect apparently 

 comparable to those due to electrolysis. A. P. 

 Trotter (London Royal Society, May 24), by ex- 

 amining the voltaic arc through a revolving per- 

 forated disk, finds that a bright spot at or near 

 the middle of the crater rapidly revolves with a 

 period seeming to correspond 'with the musical 

 hum of the arc. The author explains this ap- 

 pearance by refraction due to heated vapor. 



C.V//.S. Ostwald (" KlektKsehe Zeitung," June 

 14) regards a galvanic cell as a machine driven 

 by osmotic pressure, the voltage depending on 

 the difference of osmotic pressure of the metals 

 used that is, practically on their solubility in 

 the acid. He believes that the transformation 

 of chemical into mechanical energy will one day 



be effected more economically by the cell than 

 by combustion, the one essential being an electro- 

 lyte that will permit the necessary chemical 

 action without undergoing permanent change. 



Electrolysis. U. Behn (Wiedemann's " An- 

 nalen," January) has investigated the regular 

 deposition of silver in radial lines on a platinum 

 bowl as cathode, and considers that the lines or 

 ridges are due to convection currents set up in 

 the electrolyte by the changes in concentration 

 that go on in the liquid. W T ith silver nitrate the 

 best effect is obtained when the solution is con- 

 centrated and the current density small. In- 

 crease of temperature facilitates the formation 

 of the ridges, but electro-motive force seems to 

 have no influence. The author succeeded in ob- 

 taining the effect also with copper sulphate, lead 

 acetate, and zinc sulphate. Lehmann (Wiede- 

 mann's "Annalen," July) has observed that when 

 a solution of Congo red is electrolyzed a blue halo 

 forms around the anode and a red one around 

 the cathode. These extend gradually, and as 

 they meet a blue pigment is precipitated on the 

 side next the anode, while on the cathode side 

 the liquid becomes colorless. The author thinks 

 that oppositely charged molecules dissociated at 

 the electrodes" approach along lines of force till 

 they meet and combine. Other solutions give 

 analogous results. John Daniel (" Philosophical 

 Magazine," March), continuing his investigations 

 on the passage of ions through a thin metal par- 

 tition, and the minimum current strength re- 

 quired for polarization with such a partition 

 ("Annual Cyclopaedia," 1893, p. 621), finds that 

 the current does not sensibly affect the diffusion 

 of copper sulphate and sulphuric acid through 

 gold leaf, and that the concentration of the elec- 

 trolyte has an important influence on the critical 

 current, which appears to be proportional to the 

 conductivity. 



Condensers. Bedell and Kinsley (American 

 Institute of Electrical Engineers, Sept. 19) have 

 studied the phenomena of residual discharge in 

 condensers, and find that the condition of a con- 

 denser depends on its history for weeks or even 

 months past. In solid dielectrics the " soaking- 

 in " of the charge diminishes with increasing 

 temperature. In pure oils there is none at all. 



Electric Screens. Ayrton arid Mather (Insti- 

 tution of Electrical Engineers [England], April 

 12) find that a varnish of gelatin and glacial 

 acetic acid covered with antisulphuric enamel 

 is transparent, and at the same time so good a 

 conductor of electricity that it serves as a perfect 

 electric screen. Electric instruments whose dials 

 are covered with it are not affected by electrical 

 disturbances without. 



Reactance. This electrical quantity, as de- 

 scribed by Steinmetz and Bedell, in a paper be- 

 fore the Institute of Electrical Engineers (" Elec- 

 trical Review," July 11), is similar to resistance, 

 but the electro-motive force that overcomes it 

 consumes no power, being at right angles to the 

 current. Any electro-motive force in an alter- 

 nating circuit can be resolved into two compo- 

 nents one in the direction of the current, which 

 transmits power, and the other at right angles. 

 which overcomes the reactance. The latter may 

 be called the reactive electro-motive force, and 

 may be due to self or mutual induction, to ca- 

 pacity, or to some outside electro-motive force. 



