ABSTRACTS OF SCIENTIFIC PAPERS 355 



their Standard of Resistance, of which they issued copies during the 

 following year. 



XIII. Report [to the Royal Society] on the New Unit of Electrical 

 Resistance proposed and issued by the Committee on Electrical 

 Standards appointed in 1861 by the British Association. 'Pro- 

 ceedings of the Royal Society,' 1865, vol. xiv. ; ' Philosophical 

 Magazine,' 1865, vol. xxix. ; ' Reprint of Reports on Electrical 

 Standards,' p. 191 ; 'Anna! Phys. Chem.' 1865. 



In this Report Professor Jenkin gives an historical account of the 

 early and arbitrary units of resistance suggested or used before the 

 matter was taken up, at the suggestion of Sir "W. Thomson, by a 

 Committee of the British Association. The report goes on to men- 

 tion the system of absolute electromagnetic units, first distinctly 

 proposed by W. Weber in 1851, and accepted and extended by 

 W. Thomson immediately on its appearance, which the Committee 

 adopted as the basis of their practical electrical units. The numerical 

 relation of the practical to the absolute electromagnetic unit of 

 resistance is defined, and the experiments made to determine the 

 unit are shortly referred to. The question of permanence of the 

 standard is discussed in connection with Matthiessen's researches on 

 the electrical permanency of metals and alloys, and with the system 

 adopted by Werner Siemens of defining a standard of resistance by 

 the length and section of a column of mercury. A table is given 

 showing the relative values of the B.A. and other units, and another 

 table shows the degree of agreement in the several determinations 

 made by the Committee. 



XIV. Reply to Dr. Werner Siemens ' Paper l On the Question of the 

 Unit of Electrical Resistance.' ' Philosophical Magazine,' Sep- 

 tember 1866. 



In the ' Philosophical Magazine ' for May 1866, Dr. Werner 

 Siemens had criticised the action of the British Association Com- 

 mittee in selecting a unit of resistance based on the absolute electro- 

 magnetic system, and had advocated as unit the resistance at C. 

 of a column of mercury 1 metre long and 1 square millimetre in 

 cross section a unit actually employed by him before the Committee's 

 labours began. He had also complained that the Committee had 

 not done justice to his work. Professor Jenkin replies that the 

 scientific point in dispute involves two distinct questions, namely (1) 

 What is the best unit of electrical resistance 1 and (2) What is the 

 best method of making and reproducing any unit ? He contends 



A A 2 



