Calometric Absolute Measurements. 39 



on the duration and course of electrical currents induced by 

 current-intermissions) showed, some years later, by a series of 

 measurements. Since the question whether the induced 

 currents originated by sudden current-intermissions exactly 

 follow Ohm's law or not, cannot be theoretically decided uni- 

 versally, but only be answered empirically in each individual 

 case, I have, in order to gain a perfectly sure foundation for the 

 measurements attempted, first instituted, in a preliminary in- 

 vestigation, as severe a trial as possible of how far the currents 

 induced by sudden opening of the inducing circuit, in my 

 arrangement of the experiments, follow Ohm's law. In this 

 preliminary investigation nothing could be perceived that 

 would intimate that induced currents arising from sudden 

 current-variations do not exactly follow Ohm's law. 



If I denotes the current-intensity whose sudden diminution 

 to zero effects the induction, P the mutual electrodynamic 

 potential of the two spirals, if i represents the induced-current 

 intensity present at the moment t of the induction-process, 

 and w the resistance of the induced circuit, then is the 

 equation 



Ch 

 w\ i.dt=w.j=F.I (1) 



Jo 

 (if we suppose that the induction commences at the moment 

 t = and has already finished at the moment t=ti) the re- 

 sulting expression which is gained as soon as Neumann's 

 general law of induction and Ohm's law are applied to the 

 process of " opening "-induction. The absolute measurement 

 of w in electromagnetic measure was carried out according to 

 this equation (1). 



The electromagnetic potential of the two spirals has the 

 value 



~*dsx . ds 2 



-Jf 



COS V, 



where ds x denotes any linear element of the one spiral, ds 2 any 

 element of the other spiral, r the distance between these ele- 

 ments, and v the angle which their directions make with one 

 another, and where the integration has to be extended over all 

 the elements of both spirals. Into the somewhat lengthy 

 working-out of the calculation of the quantity P we do not, in 

 this abstract, enter further. 



The absolute electromagnetic value of the current-intensity 

 I is obtained from the deflection-angle u, measured by aid of 

 mirror, scale, and telescope : 



*-K- B - H ( 1 +m)( 1 -jJj- ta 's 



