Electromagnetic and Calometric Absolute Measurements. 31 



value of Siemens's unit would be equal to 0'9536 x 10 10 



(millimA 

 sec. / 



More recently M. Lorenz, in Copenhagen, by a very simple 

 method peculiar to himself*, in which induced currents of 

 constant strength were employed, has measured the magnitude 

 of the Siemens unit of resistance in absolute electromagnetic 

 measure, obtaining as the final result of his measurements : — 



1 S.M.U. = O9333xl0 10 / millim - Y 



\ sec. / 



How many different observers have determined the absolute 

 quantity of the Siemens resistance-unit, so many different, 

 indeed very different, results have been found. With the 

 delicacy now attained of galvanometric methods of observation, 

 with the completeness with which we believe we understand 

 the fundamental laws of current-electricity, certainly no one 

 anticipated that in the final results of physicists so practised 

 in this kind of work there could appear so great a divergency. 

 These four different results, when compared, present a new 

 problem, and one of fundamental importance for galvano- 

 metry. The two a priori equally possible solutions of the 

 problem are : — 



(a) The four observers, or groups of observers, have carried 

 out the difficult observations requisite for a determination of 

 the absolute resistance without error ; and the final results 

 differ because the natural laws assumed as the basis of the 

 different methods of observation are not precisely the true 

 ones. Or 



(6) The natural laws employed are rigorously correct, and 

 at least three of the above observers have committed some 

 error. 



In the following investigations it is found that the latter 

 solution is the true one. Three essentially different methods, 

 which brought into application three quite different natural 

 laws, and in which both rapidly and slowly varying induced 

 currents and also stationary flows came into use, have given a 

 perfectly accordant final result for the absolute value of the 

 Siemens resistance-unit — namely, 



1 S.M.U. = 0-9550 xlO 10 



(millim.N m 

 sec. / ' 



and, besides, this result agrees, except an extremely slight 

 difference, with the value obtained by the English physicists. 

 Since, even with manifold variation of my three methods of 



* Fogg. Ann. vol. cxlix. p. 251 (1873). 



