ELECTRIC DISCHARGE WITH THE CHLORIDE OF SILVER BATTERY. 161 
Fig. 37. 
The diagram, fig. 38, shows the arrangement by which, in our earlier experiments, 
we measured the resistance of a tube. The tell-tale tube* had to be substituted for 
the galvanometer in the ordinary Wheatstone bridge, as the difference of potential 
between C and D fluctuated greatly in the course of the experiment, causing violent 
swings of the needle, t 
A Z is the battery, the A terminal of which is connected at A', in the bridge 
arrangement, with two equal fluid resistance tubes, FR and Fit', of 420,000 ohms, 
placed in vessels containing ice, to keep them at a constant temperature ; an adjustable 
coil resistance is inserted between B and D ; the tube T T', to be tested, is placed 
* A tube selected for the readiness with which it permits the passage of a current of 440 cells, 
t Proc. Roy. Soc., vol. xxiv. p. 167, 1876. 
MDCCCLXXVIII. Y 
