396 
MR E. H. GRIFFITHS ON THE VALUE OF 
developed could be diminished indefinitely ; on the other hand, the conduction of heat 
between the calorimeter and the steel chamber would be increased. The wire selected 
was of pure copper (No. 21, B.W.G.), and each arm was about 10 centims. in length. 
The resistance of hM + clN was carefully determined, and found to be ‘OOSSw. It is 
probable that half the heat generated in these wares would find its way to the inner, 
and half to the outer, vessel. We may, therefore, in order to determine the heat 
thus added to the calorimeter, assume this external resistance (r) as 'OOSIoi. 
Fig. 4. 
Let II be the coil resistance. Then in any time T, the quantity of heat developed 
in the calorimeter, will be J. IT = (R + r) T. Now C = E/R, and since M and N are 
maintained at a constant difference of potential, therefore 
J.H = 
E3 
E 
therefore the effective value of the resistance = R — r (neglecting terms involving 
r~/R and higher powers of r). Since the mean vailue of R is about 8'7, the correction 
is, in any case, a small one. 
In order to test the insulation an arm of the bridge wms constructed, wLich included 
wire No. 4, the insulators, and the steel casings—good connection wuth the steel being 
insured by passing a wire into the mercury contained in the thermometer-hole. High 
battery ]30wer was used, and the resistance wms found to be greater than we could 
measure—that is, greater than 10 megohms. Since No. 4 was in connection with 
all the junctions in the plate AD, the insulation of all the junctions through the steel 
was thus established. 
The arm was then made to include No. 4, the insulators in the lid of the calori¬ 
meter, and a copper wire, wdiich wms passed dowm the glass tubes until in contact 
with the floor of the calorimeter. The resistance of the two calorimeter junctions 
was, in the same wmy, found to be greater than 10 megolnus. 
