432 H. A. Rowland—Absolute Unit of Electrical Resistance. 
Arrangement of apparatus.—Two rooms on the ground floor 
of a small building near the University were set aside for the 
experiment, making a space 8 m. long by 8°7 m. wide. e 
plan of the arrangement is seen at fig. 1. The current from 
° 1 2 2 4 5 6 7 : 
re 
the battery, in the University, entered at A, the battery being 
eighteen one-gallon cells of a chromate battery, arranged two 
abreast and eight for tension. The resistance of the circuit 
was about 20 ohms, and of the whole battery about 4 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 @ 
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, van- 
ishingly small in any case. 
At D is the principal commutator which reversed the cur- 
rent in the induction coils, L, or in the circle, F, when it: was 
in the circuit. | 
Che secondary circuit included the induction coil, L, the 
damping inductor, M, and the galvanometer G. ‘ 
t H was the Jenkin’s bridge, with standard at P, in a 
beaker of water, and a Thomson galvanometer at J K. The 
‘he telescope and scale, E, were on a jaca 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. 
