PHYSICS. 373 



Wlien the temperature of either of these deflectors changes, the little 

 astatic pair turns through an angle, which, when small, is directly 

 proportional to the temperature-diflerence. The deflections are read 

 by a mirror and lampstand, as usual. {Nature, February, 1881, xxiii, 

 372.) 



2. Electromotors. 



Thomsen has experimented to determine whether the total quantity 

 of heat which comes from the chemical reaction in a batterj' witli two 

 liquids corresponds wholly or only in part to the total heat set free in the 

 circuit. The quantities of heat evolved in the chemical reactions in the 

 Daniell cell he had previously determined to be 50130 heat-units. He 

 now finds that the total quantity of heat evolved in the circuit during 

 the decomposition of one equivalent of copper sulphate is 50292 units, a 

 difference of only 0.3 per cent. For other batteries the results were the 

 same whenever the surface of the negative electrode was not changed 

 by the electrolysis. He concludes, therefore, that the whole of the 

 chemical energy is employed in the production of electricity. ( Wied. 

 Ann., II, xi, 246; J. Phys., November, 1881, x. 502; Am. J. 8ci., January, 

 1881, III, xxi, 74.) 



Kalischer has confirmed the observations of Adams and Day, that 

 light may in certain cases set up in selenium cells a photo-electromo- 

 tive force, the cell thus becoming its own battery. {Nature, October, 

 1881, xxiv, 593.) 



Eeynier has proposed a new form of battery, in which the zinc is im- 

 mersed in a solution of sodium hydrate and the copper in a solution of 

 copper sulphate. The resistance of the battery is lessened: 1st, by 

 adding to the solutions suitable neutral salts; and, 2d, by placing the 

 zinc with its solution in a porous cup made of parchment paper without 

 seams. The electromotive force of the battery varies from 1.3 to 1.5 

 volts, and the resistance of a cell 2 decimeters high and of a cai^acity 

 of 3 liters is 0.075 ohm. {J. Phys., April, 1881, x, 160.) 



The polarization of solids in contact with liquids has received a large 

 share of attention. Helmholtz has published a paper on the currents 

 produced by the motion of electrodes of polarized i)latiuum. ( Wied. 

 Ann. xi, 737; J. Phys., July, 1881, x, 320.) Bloudlot has made an ex- 

 perimental research on the capacity of voltaic polarization. {J. Phys., 

 July, August, 1881, x, 277, 333.) Bartoli has sought to determine the 

 electromotive force of polarization produced by the passage of a known 

 current in a given electrolyte with given electrodes during a very 

 short time. {II Kuovo Cimento, III, vii, 234; J. Phys., May, 1881, x. 

 218.) 



This phenomenon of polarization has culminated in the production of 

 storage batteries, or accumulators, as they are termed. Sir William Thom- 

 son has made several communications concerning one of these, devised 

 by C. Faure, of Paris. It is essentially a Plante battery ; but in place 



