AMERICAN 
JOURNAL OF SCIENCE AND ARTS. 
[THIRD SERIES.] 
* 
Art. XLVII.—Research on the Absolute Unit of Electrical Resist- 
ance; by Henry A. RowLAND, Professor of Physics in the 
Johns Hopkins University, Baltimore, Md. 
[Continued from page 291.] 
Theory of the Method. 
WHEN a current is induced in a circuit by magnetic action 
of any kind, Faraday has shown that the induced current is 
proportional to the number of lines of force cut by the circuit 
and inversely as the resistance of the circuit. If we have two 
Circuits near each other, the first of which carries a current, 
and the second is then removed to an infinite distance, there will 
be a current in it proportional to the number of lines of force 
cut. Let now a unit current be sent through the second cir- 
cuit and one of strength E through the first; then, on removing 
the second circuit, work will be performed which we easily see 
is also proportional to the number of lines of force cut. Hence, 
if EM is the work done, Q is the induced current, and R is the 
resistance of the second circuit, 
g=cr™ 
where C is a constant whose value is unity on the absolute 
System. 
When the current in the first circuit is broken, the lines of 
force contract on themselves, and the induced current is the 
same as if the second circuit had been removed to an infinite 
distance. If the current is reversed the induced current is 
twice as great; hence in this case 
E M E 
=—2E— or R=2M—. 
pees Q 
Am. Jour. Sc1.—Turp Serres, VoL. XV, No. 89.—Mar, 1878, 
22 
