I 



238 Royal Society. 



were in progress. I cannot doubt its general correctness now, when 

 it is so decidedly confirmed by the electrometric experiments I have 

 just described, which have been executed chiefly by Mr. John Smith 

 and Mr. John Ferguson, working in my laboratory with much ability 

 since the month of November. I am still unable to explain the 

 discrepance, but it may possibly be owing to some miscalculation I 

 have made in my deductions from Weber's result. 

 Glasgow College, Jan. 18, 1860. 



Postscript, April 12, 1860. 

 I have since found that I had inadvertently misinterpreted 

 Weber's statement in the ratio of 2 to 1. I had always, as it 

 appears most natural to me to do, regarded the transference of nega- 

 tive electricity in one direction and of positive electricity in the other 

 direction, as identical agencies, to which in our ignorance as to the 

 real nature of electricity we may apply indiscriminately the one 

 expression or the other, or a combination of the two. Hence I have 

 always regarded a current of unit strength as a current in which the 

 positive or vitreous electricity flows in one direction at the rate of a 

 unit of electricity per unit of time; or the negative or resinous 

 electricity in the other direction at the same rate ; or (according to 

 the infinitely improbable hypothesis of two electric fluids) the 

 vitreous electricity flows in one direction at any rate less than a unit 

 er second, and the resinous in the opposite direction at a rate equal 

 o the remainder of the unit per second. I have only recently 

 remarked that Weber's expressions are not only adapted to the 

 hypothesis of two electric fluids, but that they also reckon as a cur- 

 rent of unit strength, what I should have called a current of strength 2, 

 namely a flow of vitreous electricity in one direction at the rate of a 

 unit of vitreous electricity per unit of time, and of the resinous 

 electricity in the other direction simultaneously, at the rate of a unit 

 of resinous electricity per unit of time. 



Weber's result as to the relation between electrostatic and electro- 

 magnetic units, when correctly interpreted, I now find would be in 

 perfect accordance with my own results given above, if the electro- 

 motive force of a single element of the Daniell's battery used were 

 2,140,000 British electro-magnetic units instead of 2,500,000, as 

 according to my thermo-dynamic estimate. This is as good an agree- 

 ment as could be expected when the difficulties of the investigations, 

 and the uncertainty which still exists as to the true measure of the 

 electromotive force of the Daniell's element are considered. It must 

 indeed be remarked that the electromotive force of Daniell's battery 

 varies by two or three or more per cent, with variations of the solu- 

 tions used ; that it varies also very sensibly with temperature ; and 

 that it seems also to be dependent, to some extent, on circumstances 

 not hitherto elucidated. A thorough examination of the electro- 

 motive force of Daniell's and other forms of galvanic battery, is an 

 object of high importance, which it is to be hoped will soon be at- 

 tained. Until this has been done, at least for Danielle battery, the 

 results of the preceding paper may be regarded as having about as 

 much accuracy as is desirable. 



