306 
MR. WHEATSTONE ON NEW INSTRUMENTS AND PROCESSES FOR 
more recent applications of the theory made by Fechner, Lenz, Jacobi, Poggendorff, 
Pouillet, &c. 
There is, however, one class of considerations which it is indispensable I should 
bring forward, because upon it are founded many of the instruments and processes 
which I shall have occasion hereafter to mention,— I allude to the laws of the distri- 
bution of the electric current in the various parts of a circuit, when a branch con- 
ductor is placed to divert a portion of the current from a limited extent thereof. 
Let X be the reduced length of the portion of the circuit from which the current is 
partially diverted, X 1 that of the wire which diverts the current, and L that of the un- 
divided part of the circuit. The force of the current in each of the adjacent con- 
ductors, X and X ', can be shown to be in the inverse ratio of their reduced lengths, 
and the reduced length of a single wire, which substituted for both would not alter 
A x! 
the force of the current, to be A + which we will designate by A. 
The force of the current in the original circuit before the introduction of the branch 
wire will then be expressed thus : 
F = 
E 
L + a’ 
and the strength of the current in the three different portions of the altered circuit 
by the following expressions : — 
In the principal or undivided portion L, 
F E E (x + a') 
r 1 L + A — L (a + a') + a x 1 ' 
In the portion from which the current has been partially diverted, or X, 
F E 
*2 “ L + A 
A 
Ea' 
L (A + A') + A A' 
In the portion which partially diverts the current, or X', 
„ E A _ Ea 
* 3 — L + A ’ IT ~ L (A +~i!) + A A'" 
§ 3 . 
It is seldom that any real advance is made in a scientific theory without a corre- 
sponding change in its terminology being required. Now that it is proved beyond 
doubt that the various sources of continued electric action differ from each other 
only in the amount of their electro-motive forces, modified by the resistance of the 
circuit of which they form part, it becomes of importance, in order to give precision 
to our statements and to avoid circumlocutions otherwise inevitable, to adopt general 
terms to express the source of a current without reference to the peculiar mode of its 
production ; I shall therefore employ the word Rheomotor to denote any apparatus 
which originates an electric current, whether it be a voltaic element or a voltaic bat- 
tery, a thermo-electric element or a thermo-electric battery, or any other source 
