376 Prof. J. J. Thomson and Mr. G. F. C. Searle. [Mar. 27, 



merits determined by harmonics of any even degree (n), the " coefficient 

 of stability" for the displacement symmetrical abont the axis is the 

 last, to change sign, it is clear that hardly any less general constraint 

 would suffice to produce such a result. 



VI. "A Determination of " v" the Ratio of the Electromagnetic 

 Unit of Electricity to the Electrostatic Unit." By J. J. 

 Thomson, M.A., F.R.S., Cavendish Professor of Experi- 

 mental Physics, Cambridge, and G. F. C. Searle, B.A., 

 Peterhouse, Demonstrator in the Cavendish Laboratory, 

 Cambridge. Received March 12, 1890. 



(Abstract.) 



The experiments made by one of us in 1883 having given a value 

 for considerably smaller than those found in several recent 



researches on this subject, it was thought desirable to repeat the 

 experiments. The method used in 1883 was to find both the 

 electrostatic and the electromagnetic measures of the capacity of a 

 condenser, the electrostatic measure being calculated from the 

 dimensions of the condenser, and the electromagnetic measure by 

 determining a resistance which would produce the same effect as that 

 produced by repeated charging of the condenser when placed in one 

 arm of a Wheatstone's bridge. In the experiments in 1883 the 

 condenser used in determining the electromagnetic measure was not the 

 same as that for which the electrostatic ^capacity had been calculated, 

 but one without a guard ring, the equality of the capacity of this 

 condenser and the guard ring condenser being tested by the method 

 given in Maxwell's ' Electricity and Magnetism,' vol. 1, p. 324. 



In repeating the experiments we adopted at first the same method 

 as before, using, however, a key of different design for testing the 

 equality of the condensers by Maxwell's method. We got very 

 consistent results, practically identical with those obtained in 1883. 

 We may mention here, since it has been suggested that the capacity 

 of the leads might explain the low value of " v " obtained previously, 

 that the leads are allowed for by the way the comparison between the 

 two condensers is made, for the same leads are used in the determina- 

 tion of the electromagnetic measure of the capacity of the auxiliary 

 condenser and in the comparison of the capacity of this condenser 

 with the one with the guard ring, and the capacity of the auxiliary 

 condenser is adjusted until its capacity, plus that of the leads, equals 

 the capacity of the guard ring condenser ; and in the electromagnetic 

 measurements it is the capacity of the auxiliary condenser, plus that 

 of its leads, which is found. 



