356 ABSTRACTS OF SCIENTIFIC PAPERS 



that there is no reason to adopt Dr. Siemens's definition more 

 than any other ; and that, on the other hand, the absolute system 

 of units is of great convenience in dealing with the relations of 

 electrical magnitudes to one another and to other quantities in 

 dynamics. He then points out that as regards reproduction it had 

 not been shown that a mercury unit could be reproduced with 

 greater accuracy than the B. A. unit, and that as regards permanency 

 the method practised by the Committee gave all the guarantees that 

 Dr. Siemens's plan could give, and more. The last part of the paper 

 refers at length to the historical and personal question raised by 

 Dr. Siemens, and in it Mr. Jenkin, while acknowledging fully the 

 independent invention by Dr. Siemens of many methods in electrical 

 measurement and his successful reduction of them to practice, claims 

 ' for Professor Thomson the honour of having been the first to insist 

 on a measurement of the conducting-power of the copper in sub- 

 marine cables, and to express the quality of the insulation in terms 

 of resistance.' 



XV. On a Modification of Siemens's Resistance- Measurer. Appendix 

 II. to the Fifth Report of the Committee on Electrical Standards. 

 'British Association Report for 1867,' p. _481 ; 'Reprint of 

 Reports on Electrical Standards,' p. 144. 



The Resistance-Measurer of C. W. Siemens (described in Ap- 

 pendix I. to the same Report) was a species of differential galvano- 

 meter with two coils, one on either side of the magnet, and capable 

 of being moved so that one receded from the magnet while the other 

 approached it. In Jenkin's modification the two coils are set at 

 right angles to each other, the magnet being at the centre of both, 

 and the coils are capable of being turned together on a horizontal 

 plane. A current is divided through them, and through the known 

 and unknown resistance respectively, and the coils are turned until 

 their electromagnetic effects on the needle neutralise one another. 



XVI. Experiments on Capacity. Appendix IV. to the Fifth Report 

 of the Committee on Electrical Standards. ' British Association 

 Report for 1867,' p. 483 ; ' Reprint of Reports on Electrical 

 Standards,' p. 146. 



This paper is interesting as an account of the earliest attempt 

 to form a standard of electrostatic capacity, based on the electro- 

 magnetic system of units. Practical electricians had previously 

 constructed condensers of arbitrary capacity, equal to that of a knot 



