VALUE OF THE BRITISH ASSOCIATION UNIT OF RESISTANCE. 
2D f J 
included a sawdust Daniell (L) and a resistance coil of 100 ohms (M). By shifting- 
one of the binding screws, the galvanometer reading, in the absence of the main 
battery current, and after attainment of the proper speed, was made to be nearly the 
same as when the galvanometer contact was broken. 
§ 8. The general plan of the connexions and the modus opercmdi will now be 
intelligible from fig. 2. The poles of the battery A, consisting of 20 Daniell cells, 
were connected with a mercury reversing key B, the two positions of which were 
distinguished by the letters E and W (east and west). From thence the current 
passed through the induction coils C ancl the equivalent resistance R, of which the 
details are reserved for the moment. The reflecting galvanometer, G, is placed at a 
considerable distance in order to avoid the direct influence of the coils, and is connected 
with the inner sliding contact, F. Its resistance is about \ ohm ; and by the aid of 
the compensating magnet the vibrations of the needle were made slow enough to be 
readily observed. The terminals of the galvanometer branch, which includes also 
a commutator, I, are connected to the extremities of the resistance, R. 
If, while the disc is maintained in uniform rotation, the reading of the galvanometer 
is the same whichever way the battery key may stand (correction being made, if 
necessary, for a direct effect upon the needle), it is a proof the contemplated balance 
is actually attained. In this way all disturbance from the earth’s magnetism, and 
from thermo-electric forces whether situated at the sliding contacts, or within the 
resistance coils of which R is composed, or at any other part of the galvanometer 
circuit, is eliminated from the result. The adjustment is effected by varying a 
comparatively large resistance, taken from a box, and placed in multiple arc with 
one of the components of R. 
2 Q 2 
