THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



SEPTEMBER 1866. 



XXII. Reply to Dr. Werner Siemens's Paper " On the Question 

 of the Unit of Electrical Resistance." By Eleeming Jenkin, 

 F.R.S.* 



IN the Philosophical Magazine for May, there appeared a trans- 

 lation of a paper " On the Unit of Electrical Resistance " by 

 Dr. Werner Siemens, containing views much at variance with the 

 conclusions of the British- Association Electrical- Standard Com- 

 mittee, and referring frequently to the part I have taken in sup- 

 porting those conclusions. Dr. Siemens enjoys so high a repu- 

 tation, that I am anxious to answer his arguments directly, in- 

 stead of simply referring, as I might do, to the Reports of the 

 Committee, where most of the points have, I think, been already 

 met. 



Dr. Siemens has treated of several very distinct questions, 

 which might be divided as follows : — 



(1) What is the best unit of electrical resistance ? 



(2) What is the best method of making and reproducing any 

 unit? 



(3) Have Dr. Siemens' s proposals and labours met with fair 

 consideration and full acknowledgment by the Committee and by 

 myself ? 



As to the first point, Dr. Siemens supports as unit the resist- 

 ance of a prism of mercury 1 metre long and 1 square millimetre 

 section at 0° C, or a million times the resistance of a cubic metre 

 of mercury at C . 



The British- Association Committee propose as unit ten million 

 times the absolute electromagnetic unit, or metre per second, as 



* Communicated by the Author. 

 Phil May. S. 4. Vol. 32. No. 215. Sept. 1866. M 



