ON THE ABSOLUTE UXIT OF ELECTRICAL EESISTANCE 



171 



resistance of the circuit was about 20 ohms, and of the whole battery 

 about ^ ohm, thus insuring a reasonably constant current. 



At B some resistance could be inserted by withdrawing plugs so as 

 to vary the current. 



At C is the tangent galvanometer with commutator on a brick pier. 

 The nearness of the commutator produces no error, seeing that we only 

 wish to determine the ratio of two currents. The effect of currents in 

 the commutator was, however, vanishingly small in any case. 



At D is the principal commutator which reversed the current in the 

 induction coils, L, or in the circle, F, when it was in the circuit. 



FIG. 1. 



The secondary circuit included the induction coil, L, the damping 

 inductor, M, and the galvanometer 0. 



At H was the Jenkin's bridge, with standard at P, in a beaker of 

 water, and a Thomson galvanometer at J K. The secondary circuit 

 could be joined to the bridge by raising a U-shaped piece of wire out of 

 the mercury cups. 



The telescope and scale, E, were on a heavy wooden table, and the 

 two galvanometers on brick piers with marble tops. 



A row of gas-burners at Q illuminated the silvered scale in the most 

 perfect manner. 



Adjustments and tests. The circle, F, must be parallel to coils of 

 galvanometer, G. The circle and coils of galvanometer were first 

 adjusted with their planes vertical and then adjusted in azimuth by 



