PHYSICS. 485 



tive force was measured on Thomson's potential galvanometer, a high- 

 resistance Thomson galvanometer and a condenser being used to check 

 the indications. The i)hotometric power of the lamps, both arc and in- 

 candescent, was determined in terms of an Edison 10-candle lamp taken 

 as a standard. The efficiency found for the Thomson-Houstou arc dy- 

 namo was 81.5; of the Weston arc dynamo, 8G.5 ; of the Weston in- 

 candescent dynamo, 87.9 ; and of the Edison incandescent dynamo, 95.1. 

 In the case of the arc lamps the jury found a difference of more than 40 

 l)er cent, in favor of the Thomson-Houstou, and in that of incandescent 

 lamps they found a difference of 25 per cent, of light per electrical 

 horse-power in favor of the Edison. {Science, February, 1884, iii, 174.) 



5. Electro-chemical Decomposition. 



Jahn, in a paper communicated to the Vienna Academy, has shown 

 that in the electrolysis of solutions of copper sulphate and of zinc sul- 

 phate between two electrodes of platinum, the quantities of heat which 

 become free during the decomposition of equivalent weights of the two 

 salts are inversely as the quantities of heat evolved during tlie foruiation 

 of these salts by means of the two metals, of oxygen and of sulphuric 

 acid. (J. Phys., June, 1884, II, in, 274.) 



Warburg has succeeded in electrolyzing glass by heating it to 300o 

 between mercury electrodes. The glass used was a soda-lime glass, 

 which is a conductor at this temperature. The current of 15 to 30 Bun- 

 sen cells was used, and at first passed freely ; but in a few moments the 

 current diminished, and in the course of an hour fell to tooo, from the for- 

 mation at the anode of a layer of insulating silica. Tbis siliceous layer 

 acted as the dielectric of a condenser between two conductors ; and by 

 charging it with from 5 to 20 Bunsen cells, the condenser was found to 

 have a capacity of from 0.021 to 0.041 microfarad, according to the 

 thickness of the layer. If sodium amalgam be used as the anode, no 

 layer of silica results, but sodium is found in the mercury on the cath- 

 ode side, the amount of which was found to agree with the weight of 

 silver deposited in a voltameter in the same circuit. Potassium amal- 

 gam is witliout action. {J. Phys., October, 1884, II, in, 452 ; Phil. Mag., 

 August, 1884, V, xviii, 159.) 



Gore has propounded a theory of the relation of heat to ele(;trolysis 

 which assumes that metals and electrolytes are throughout their masses 

 in a state of molecular vibration; that the molecules of these sub- 

 stances, being frictionlcss bodies in a frictionless medium, and their 

 motion not being dissipated by conduction or radiation, continue inces- 

 santly in motion until some cause arises to prevent them ; that each 

 metal or electrolyte wlien unequally heated has to a certain extent an 

 uidike class of motions in its differently heated parts, and behaves in 

 those parts somewhat like two metals or electrolytes, and those unlike 

 motions are enabled, through the intermediate conducting portion of 

 the substance, to render those parts electro-polar; that every different 



