Electromagnetic to t7ie Electrostatic Unit of Electric Quantity. 279 



therefore though tdesirable by the Committee of the British 

 Association, when appointed in 1861 to consider the question 

 of the selection of electrical units, that they should decide on 

 some system not only independent of any particular material, 

 but also of such a nature that every simple equation connecting 

 the absolute measurements of force, work, electric and mag- 

 netic quantity, current, resistance, and electromotive force 

 should be independent of numerical coefficients. 



But there are, as is well known, six fundamental equations 

 connecting these six quantities — 



3. q = ct, 

 elm 



5. iv=zc 2 rt, 



4 f— 



r e 



0. c = -, 



r 



one equation in fact more than is necessary to produce a single 

 system of units. The consequence is that one or other of the 

 two similar equations, Nos. 1 and 2, connecting electric or mag- 

 netic quantity with force must be rejected. If we reject No. 2, 

 then 1, 3, 4, 5, 6 determine the electrostatic units of quantity, 

 current, magnetic pole, resistance, and electromotive force; and 

 by rejecting No. 1, then 2, 4, 3, 5, 6 determine the electro- 

 magnetic units of magnetic pole, current, quantity, resistance, 

 and electromotive force. The names " electrostatic " and 

 " electromagnetic " refer of course only to the fundamental 

 conception of the two systems, and do not in any way imply 

 that in these systems the electricity must be in rest or 

 motion : thus, for example, we may have an electrostatic unit of 

 current. 



Nature of u y" and the importance of Measuring its Value, 

 The object of the investigation described in this paper is to 

 determine the value of " v" the ratio of the electromagnetic 

 to the electrostatic unit of quantity ; but it may be asked, since 

 measurements in electromagnetic units are alone employed by 

 telegraph-engineers, what interest has such an investigation 

 or its results to them ? The answer is, We cannot, from the 

 nature of an electromotive force, have a standard cell of the 



