Measurements of Inductance. 



521 



the following discussion, and most o£ the ordinary laboratory 

 methods are dealt with. 



§ 2. Maxwell's original plan for comparing an inductance 

 with a capacity forms a convenient starting-point, since it 

 illustrates all the principles simply, although the double 

 adjustment needed makes it unworkable in practice. The 

 diagrams show the symbols employed: Gr, g are respectively 



the resistance and inductance of the galvanometer, and the 

 letters x, y, z, u denote quantities which have flowed in the 

 respective arms since some initial moment. If this is the 

 moment of completing the battery circuit, we have 



E-LS = (P + B + R)i? + By-R*, 

 ^=B£-Sy-(G-+R-t S)ir + Sw, 

 E==B£+(Q + S + B)y'+S?-S*> 



Integrating the first two, and putting the symbol D for the 



d 

 operation -=- , we find that as, y, z, u and t are proportional 



respectively to the five determinants arising from these 

 equations. But it scarcely affects the numerical results 

 (since B is negligible) if the initial moment is that of sliort- 

 circidting the battery, and this makes the computation some- 

 what simpler. If we put / for the steady current in the 

 arm P, the equations are 



(LD + P + R>-Rs-L/=0, 

 R*-Sy-(0D + G + R + S> + Stt=O, 



KSDy + KSD*-(KSD + l)w-KB/=0. 



