12i 



EEPOKT — 1894. 



Rayleigh in his determination of the ohm by the method of Lorenz (see 

 tig. 1). . 



If there is no current through the galvanometer, there is equality 

 between the E.M.F. due to the rotation of the disc in the field of the 

 standard coil and the E.M.F. due to the current through R^ ; and we 



R„ Ro, 10-ohm coils. 

 K3, R,, ■1-ohm coils. 



B, Battery. 



G, Galvanometer. 



D, Rotating disc. 

 K K, Standard coil. ' 



liave, if Ri, Rj, R3, R4 are the values of the four resistance coils in 



international ohms, and if 

 absolute measure, 



X is the value of the international ohm in 



RaR^"*^ 



-=Mn, 



Rl +R2 + I^3 + I^4 



where M=the coefficient of mutual induction of the standard coil and 

 the circumference of the disc, and »i = the rate of rotation of the disc. 



The resistance coils are of B.A. pattern. They were immersed in 

 water, and the temperatures of thermometers within the coil frames were 

 read before and after each observation. A wooden box surrounded the 

 four cans containing the coils. 



The method of making the observations was the same as that described 

 in the paper I read before the Section last year (vide Electrical Standards 

 Committee Report, 1893). 



The results are as follows, the figure in each case giving the value of 

 the international ohm in true ohms. 



Jtily 7. — Standard coil carefully adjusted. Three-minute tapes. 



■999703 



•999761 



•9 99807 



Mean . -999757 



July 9. — No readjustment of standard coil. One-minute tapes. 



•999757 

 •999711 

 •999683 

 •999782 



Mean 



•999733 



