256 THOMPSON YATES LABORATORIES REPORT 
considered. The remaining pieces of nerve AB and CD are treated, for the purposes 
of calculation, as if they were a continuation of the terminal conductors of the galvan- 
ometer and compensator circuit up to the points B and C. 
ABC D 
According to Helmholtz's principle the closure of the key K gives rise to a 
current in the complete circuit KBC, the magnitude of which is determined by the 
source of EMF, which is of the value of the pre-existing difference of potential 
between points BC, and by the total resistance in this circuit BCK. 
It should be possible to determine the resistance of any portion of this circuit 
when the current is traversing it from a discovery of the difference of potential 
existing then between the terminal points of the resistance. 
In this way it is possible to determine the longitudinal resistance between B and C } 
using as ' leads ' to the terminals of this resistance the pieces of nerve AB, CD. 
e 
r = R. 
E 
Where E = "00448, the pre-existing potential differences between points BC. 
R = 10,700 + 6,000 = 16,700 ohms, 
e = the newly-found potential difference between B and C. 
= pre-existing potential difference between points AD — new potential difference 
between AD. 
= -01450 — -01305 = -00145 Daniell. 
e 
r = R. 
E 
•00145 
= x 16,700 ohms. 
•00448 
= 5,405 ohms. 
This value, obtained from this experiment, for the ' longitudinal resistance ' 
between points B and C closely agrees, as a reference to the data of case (c) shows, 
with the value as otherwise calculated and used as the basis of the calculations made 
in case and case (7>), namely, 
5,200 ohms. 
The agreement of experimental results and prediction are so close in these 
experiments that one is inclined to place confidence in the measurements upon which 
the simple calculations depend, and one is, therefore, inclined to draw further 
conclusions from them. 
