THE MECHANICAL EQUIVALENT OF HEAT. 
399 
Table IV. 
R = {(N, + N 3 ) - (Ni + N4)1/2. 
A large number of similar observations were taken at temperatures ranging from 
13° to 26° C. Observations at certain temperatures were repeated at regular 
intervals, and no change of any kind could be detected. The resulting resistance 
curve was the characteristic platinum one, and in no way differed from those given 
by our platinum thermometers. This in itself seems to us to be an adequate proof 
that the insulation of the coil was sufficient. 
On September 4, the calorimeter was taken to pieces, and the method of fastening 
the wire to the glass rods within the calorimeter was altered. The wire was a little 
strained during the operation ; but the only effect was to slightly increase its resist¬ 
ance at all temperatures. A new resistance curve, however, had to be drawn, and 
new values of II used after that date. 
It may be mentioned that this coil was often used by us as a platinum thermometer 
to determine the temperature of the calorimeter when below, or above, the range 
of E,,. 
The reversing keys in the storage and Clark cell circuit (see fig. 2, p. 332) were 
of the ordinary “rocker” form, but so constructed that as the wires on one side 
passed out of the mercury cups, the wires on the other almost immediately made 
* See Section X. The mercury thermometer E,„ was used throughout all observations on the 
temperature of the calorimeter. 
