﻿298 Dr. S. R. Milner on the Use of the Secohmmeter 



fails to give an easily interpretable result. Cases in point 

 are the determinations of (1) the resistance of an electrolyte 

 between small electrodes which become appreciably polarized 

 in a smaller time than that elapsing between successive re- 

 versals of the battery; (2) the surface capacity of electrodes 

 in a solution the resistance of which is not negligible; (3) the 

 capacity of a condenser which has an appreciable leakage, 

 such as is used in determining the S.I.C. of poorly insulating 

 materials. Here we are dealing with what is equivalent to 

 a resistance and a capacity combined in such a way that they 

 cannot be taken apart and measured separately. (1) and (2) 

 may be looked on as a combination in series, (3) in parallel, 

 of a resistance and a capacity with each other. For the 

 accurate determination of the members of such a combination 

 by the TTheatstone's bridge, each must be individually balanced 

 by that of a similar combination in one of the other arms. 

 The balancing thus requires the adjustment of two variables 

 instead of one, and this is a very difficult operation in practice 

 unless the two adjustments are independent of each other. 

 Nernst has shown that with the telephone the two adjustments 

 can be made independently by reason of the fact that the 

 loudness of the sound becomes a minimum when one member 

 of the combination is balanced independently of the value of 

 the other. With the secohmmeter, however, the two adjust- 

 ments are not independent of each other in general, although 

 they become so under certain conditions which are elucidated 

 in the present paper. In some recent measurements of the 

 kind included in classes (1) and (2), I found a telephone was 

 wholly unavailable by reason of its want of sensitiveness. 

 An investigation in some detail of the theory and practice of 

 the use of the secohmmeter for the purpose, showed that 

 methods for adjusting to the double balance, as simple and 

 effective as those of JSTernst with the telephone, although 

 based on different principles, were available with the secohm- 

 meter. As the instrument will probably be used more and 

 more in the future in view of its superiority in sensitiveness 

 to the telephone, it is hoped that a description of these may 

 be of value. 



In fig. 1, S and K are an unknown resistance and capacity 

 supposed inseparably connected in series and forming one 

 arm of a Wheatstone\s-bridge system ABCD. P, Q, R, F, 

 and /are the remaining resistances of the bridge, and H is a 

 known capacity in series with R. X and Y are the commu- 

 tators of the secohmmeter, show r n separately, but really 

 mounted on the same axle. Each reverses the current passing 

 through it four times during a complete revolution of the 



