PHYSICS. 499 



biudiug screws with a mirror galvanometer. The strength of the shunt 

 current varies as the bridge is displaced. {Nature, June, xxvi, p. 139.) 



Von Fleischl has claimed this apparatus as having been constructed 

 by him in 1877, and described under the name "rheonom." He says it 

 has been in Prof. E. Du Bois Reymond's cabinet for more than five years. 

 {Nature, December, xxvii, p. 127.) 



Stone has constructed an electrodynamometer, in which the suspended 

 coil was made of aluminum wire, was 1^ inches internal diameter, 

 contained forty-two turns of wire in five layers, weighed 6^ grams, and 

 had a resistance of half an ohm. Its performance was satisfactory. 

 {Nature, June, xxvi, p. 201.) 



Slotte has given a method for calculating the length of the platinum 

 wire belonging to the Wheatstone bridge (which cannot always be deter- 

 mined by direct measurement), which is founded on that of comparing 

 and exchanging resistances. {Wied. Ann.,Y, xv, p. 176; Phil. Mag., 

 March, V, xiii, p. 227.) 



Sloguinoff has contrived a simple form of compensator for use with 

 the method of Du Bois Reymond for measuring electromotive forces by 

 the method of compensation. Two wires of equal length are stretched 

 parallel to one another and connected together at one end. To the 

 other ends a standard cell is connected. To one of these same ends one 

 wire of the battery to be tested is connected, a galvanometer being in 

 the circuit, the other battery wire being attached to the end of a third 

 wire parallel to the others. Across the three wires is a slider for ad- 

 justing the distance. {J. Phys., March, II, i, p. 138.) 



The International Electrical Congress adojjted the ohm as the unit 

 of resistance and defined it to be 10^ c. a. s. units. But they left to a 

 special commission the determination of the length of a prism of mer- 

 cury one millimeter in cross-section which should have this resistance. 

 In consequence a large number of important papers has been published 

 upon the best method of making this measurement; or, what is practi- 

 cally the same, of determining the actual value of the B. A. unit called 

 the ohm. Before the meeting of the Congress, Rayleigh and Schuster 

 had repeated the original determination, using Thomson's method and 

 the identical apparatus with which the B. A. Committee worked. They 

 find that the standard called an ohm by the committee is 0.9893 x 

 10^ c. a. s. units; a value near that obtained by Rowland, 0.9911 x 10^ 

 {ProG. Roy. Soc, April, 1881 ; J. Phys., January, II, i, p. 43.) 



Joubert has suggested a method for the determination of the ohm 

 founded on the measurement with the electrometer of the electromotive 

 forces in an induced circuit. {Compfes Rendus, June, xciv, p. 1519.) 



Lippmann has proposed a thermoscopic method for the determination 

 of the ohm, which requires no measurement of amount of heat, nor an 

 exact value of Joule's equivalent. ( Gomptes Rendus, October, xcv, p. 634.) 

 The various other methods which have been jjroposed have been dis- 

 cussed by Lippmann (J. Phys., July, II, i, p. 313); by Lorenz {J. Phys.^ 



