194 "' OUTLINES OF PHYSICAL CHEMISTEY
since they are directly connected with a thick wire. But as we go towards the right or towards the left the poten- tial-difference increases. If we consider, for example, the volt.
Suppose now that in the branch circuit (fig. 44) we have:
1. The element w under examination, in opposition to the principal current coming from e.
2. A Lippmann electrometer, l. 8. If necessary, one or more standard 1-volt elements,
a, b, c, d, e, /, in opposition to the element w.
4. A commutator by which the electrometer can be closed on itself or by which the circuit can be closed by interposing the electrometer.
The ends a and /3 of the secondary circuit are so con- nected on the resistance a b that when the circuit is closed of equilibrium. One succeeds in this after a few trials. respectively as in the figure, then the electromotive force measured is 1*16 volt, because it is necessary to take the standard 1-volt element a, which is in opposition to *-, into consideration.
Measurement of Besistance :
Wheatstone Bridge Method
The arrangement of the Wheatstone bridge is diagram- matically represented in fig. 45. At the points a and b the potentials are p and p', and two points c and d having the same potential p are connected by the bridge (in which there is a galvanometer) ; and let us suppose that the resistances of the four branches thus formed are r and /, b and b'.
��standard cell is so arranged that its current is opposed to the current from e. The resistance b is then altered until the electrometer denotes potential-equilibrium at a and b.
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