Electrostatic Units in the Electromagnetic Unit. 227 



value of R tan a what Mr. Shida says it is. In the first case 

 we have — 



06. 



tan » 



r. 



E. 



R tan a,. 



o / 



45 15 

 42 45 

 51 39 



1-0088 

 0-9244 

 1-2639 



75 

 80 

 50 



107-88 



112-88 



82-88 



108-83 

 104-35 

 104-75 



Mean . . . 



= 105-98 



whilst in the second case we have 



ct. 



tana. 



r. 



R. 



R tan x. 



45 15 

 42 45 

 51 39 



1-0088 

 0-9244 

 1-2639 



80 



100 



50 



112-88 



132-88 

 82-88 



113-87 

 122-84 

 104-75 







Mea 



n . . . 



= 113-82 



In either case the values of R tan a are very far from being 

 constant, whilst the mean value materially differs from 104*73 

 ohms. 



Two other slips, presumably made either in transcribing or 

 during proof-corrections, have been already noticed, viz. the 

 statement (in each paper) that the electrostatic values of the 

 electromotive forces of the battery and cell employed were 

 0-904187 and 0-034380 C.G.S. units, instead of one tenth of 

 these quantities in each case respectively. 



Whatever may be the explanation of these numerical aber- 

 rations, it is at least evident that when an author twice over 

 publishes such numbers as these (and only such numbers) as 

 samples of his work, he can hardly be surprised if readers con- 

 ceive it to be possible that oversights may have been made in 

 other portions of the research, especially when incomplete or 

 ambiguous descriptions are given tending to convey the im- 

 pression that oversights were actually made. Humanum est 

 errare. 



In conclusion, I must remark that Mr. Shida misrepre- 

 sents me when he says that I call the difference of poten- 

 tial, V— V, subsisting between the poles of an electromotor 

 which is generating a current, the E.M.F. of that electro- 

 motor. On the contrary, I expressly define (Phil. Mag. May 

 1881, p. 359, footnote)' the E.M.F. of such an electromotor, E, 



