PHYSICS, PROGRESS OF, IX 1896. 



643 



among physicists regarding what is properly to be 

 termed (lie " resi-i.-iinv " in such a case, and the ne- 

 v for a modification of definitions was aeknowl- 

 1. "The Electrician " (London, July 8), in an 

 editorial on the .subject, concludes that "negative 

 iv-i-tatice" and "adjuvant distributed elect ro-mo- 

 tive force" are one and the >ame thing, and since 

 the latter is possible and actually occurs, -o may 

 the former. Fitz Gerald (ibid.. July 17) thinks that 

 the whole question is simply one of convenience 

 of definition. He prefers the term "adjuvant 

 Thompson effect '' for any distributed thermal ac- 

 tion that helps the current. 



Eh-ctro-motin Force. Bancroft ("Physical Re- 

 view." January-February) concludes from a dis- 

 -ion of various experiments that the potential 

 difference between a metal and an electrolyte does 

 not depend, except in special cases, on the concen- 

 tration of the solution nor on the nature of the 

 positive ion, but on the electrode, the negative 

 ion, and the solvent. Campbell (London Phys- 



rical Society. June 12) advocates the use of air- 

 coil transformers for measuring alternating volt- 

 ages and currents that are either above or below 

 the range of available instruments. Since the 

 readings depend on the frequency, when the volt- 

 age is observed on an open-circuit secondary, in at- 

 tempting to measure the current in the primary of 

 such a transformer. Mr. Campbell uses a closed 

 secondary with very high inductance, in which case 

 the primary current is proportional to the second- 

 ary, which may be measured with an ammeter. 



'Specific Inductive Capacity. Silberstein (Wie- 

 demann's "Annalen," December. 1895) has shown 

 that the specific inductive capacity of a mixture of 

 two perfectly insulating liquids which mix in all 

 proportions and do not contract in the p 

 may be found by taking the sum of the products 

 of the respective separate volumes by their specific 

 inductive capacities and dividing by the total 

 volume. 



Ctji-nhn*ers. Carpenter (" Physical Review." No- 

 vember-December) finds that the so-called "soak- 

 ing in " of a condenser charge varies greatly in 

 rapidity with different condensers, and seems also 

 to depend somewhat on the potential of charge, but 

 not on the potential difference. 



Dielectrics. Duff (' Physical Review." July-Au- 

 gust) finds that the viscosity of glycerin, castor oil, 

 and other nonconducting liquids is increased by 

 less than 1 per cent, when the liquid is subjected to 

 considerable electrostatic stress. The phenomenon 

 seems related to the electrostatic Kerr effect. 



Cells. Jacques ("Boston Herald." May 11; 

 "Electrical Review." May 20, etc.) has devised 

 what he calls a " carbo-electric battery." consisting 

 of a carbon anode and an iron cathode in a bath of 

 fused caustic soda or potash through which air is 

 continually blown. He asserts that the resulting 

 current is due to true combustion of the carbon, 

 and that he has therefore succeeded in obtaining 

 electricity direct from coal. Some of his critics re- 

 gard the device as a thermoelectric battery that 

 owes its power to the heat energy used to keep the 

 soda fused. Stockbridge (' Engineering Magazine,'' 

 July) describes the cell as consisting of an iron pot 

 of fused caustic soda in which hangs a carbon rod. 

 When the cell is in action the soda must be at a 

 temperature of 400 : to 500' C.. and air is pumped 

 through it. The carbon is attacked and gradually 

 consumed, with the generation of a current. The 

 cell is said to have an efficiency of 85 per cent., but 

 this does not take into account the expenditure of 

 heat for keeping the soda fused or the power that 

 runs the air pump. Reed ("Electrical World," 

 Aug. 8) regards the cell as neither galvanic nor 

 thermoelectric, and thinks that its action is what 



In- calls " thermotropic." depending on the princi- 

 ple that if between two similar picc.^ of metal there 

 is an oxide of the metal or any other connecting . 

 oxide or salt not decomposed by the ilame. upon 

 heating either of the wires while keeping the other 

 cool, a strong electric current flows through the 

 circuit. On transferring the heat from one piece to 

 the other the direction of the current is reversed. 

 The electro-motive force from two copper wires 

 with their junction is at lea-t 100 times that of an 

 ordinary thermoelectric couple. Koehne. in Ger- 

 many, has carried on similar investigations, and 

 concludes that a solution of carbon may be obtained 

 electrolytic-ally, that carbon can be separated from 

 it at the cathode, and that a cell may be made hav- 

 ing carbon as its soluble electrode. He describes 

 (Berlin Phy.-ical Society. Feb. 14) his success in ob- 

 taining such a solution by using pure carbon as 

 anode, platinum as cathode, and hot sulphuric acid 

 as the electrolyte. The fluid became successively 

 yellow, brown, and black, and graphite was de- 

 posited on the cathode. 



The Electric Arc. Fleming and Petavel (London 

 Physical Society. Feb. 28) find, from an analytical 

 study of the alternating-current arc, that the purple 

 light of the true arc varies periodically, being com- 

 pletely extinguished for a certain interval during 

 the phase. It has equal maximum values during 

 the period, lagging slightly behind the maximum 

 expenditures of power in the arc. The illuminating 

 power of the carbon crater varies between a mini- 

 mum and two unequal maxima, one when the carbon 

 is positive and the other just behind the instant of 

 greatest power expenditure. The total mean spher- 

 ical candle power is less for equal expenditure of 

 power than in the continuous-current arc, and low- 

 ering the frequency decreases the efficiency. Frith 

 (London Physical Society. April 24) finds that an 

 arc has the power of modifying the wave form in 

 an alternating circuit in which it is included. The 

 difference between the efficiency of such arcs in the 

 laboratory and that which is claimed for them in 

 practice may thus be explained. Arons (Wiede- 

 mann's " Annalen," January) suggests that the diffi- 

 culty of producing an alternate-current arc between 

 metallic electrodes may be due to the lower thermal 

 conductivity of carbon, which enables it to retain 

 its heat, or to the volatile gases given off by carbon, 

 or to the oxidation of metals during the passage of 

 the current. 



Electrolysis. Zelinsky and Krapiwin ("Zeit- 

 schrift fiir physikalische Chemie," October) have 

 investigated the electrolytic conductivity of solu- 

 tions of salt in methyl alcohol and find that in 

 many cases these have conductivities of the same 

 order of magnitude as aqueous solutions. In all 

 cases the molecular conductivity increases with di- 

 lution. The substitution of a little alcohol for 

 water in the aqueous solutions has precisely the 

 same effect as the substitution of a little water for 

 alcohol in the others, namely, a diminution of con- 

 ductivity. Xo explanation of this has yet been 

 suggested. Tommasi (Paris Academy of Sciences, 

 May 18) has devised a new apparatus for elec- 

 trolysis in which polarization is suppressed, the de- 

 posited metal is removed from the oxidizing action 

 of the bath, and the resistance is reduced. 



Thermoelectricity. Hagenbach (Wiedemann's 

 "Annalen." May) rinds that a thermo-couple of cad- 

 mium or lead amalgams or salts shows a diminution 

 as dilution is increased, contrary to the general rule 

 and to theory. 



Contact Electricity. Nernst (Wiedemann's " An- 

 nalen," Augtist) has put forth a theory of contact 

 electricity based on ionic velocities. An accumula- 

 tion of electricity can be prevented only by the 

 equally rapid diffusion of both ions of an electro- 



