448 PROFESSOR A. SCHUSTER AND MR. W. GANNON ON A 

—(%) = 2p /t fort < T 
IZ] o a. T 

ole) D_ (fi — /t —T) fort > T 
a 
T/Ow pt” 
ee = Ae 
(es eS: An/ 7 
| 

In our experiments the average time ¢ during which the rate of cooling was 
observed was with sufficient accuracy equal to 2T, reckoned from the moment the 
heating began. In that case, the above formule show that the total amount of heat 
which has passed into the thermometer, denoting by A the area of its cross-section, is 
An ApT*” 
3a,/7 [2 V2 ine 1]; 
while the heat lost to the calorimeter, calculated by means of the cooling during the 
last. period, is 
Se Apie 
ar/ ly 3 = Wh 
The quantity to be added to the water-equivalent is obtained by dividing the 
difference of these values by pT, and becomes therefore 
Nhe Far Ness YEE 
= wie (5 — /2)=12—— 
a 7 
oa 7 

Substituting for @ in terms of the conductivity «, the capacity for heat of unit 
volume of glass s, this becomes 1:2 A ,/(«sT/z). 
Putting in the numerical values corresponding to our experiments « = 00021, 
T = 540, s =°5, A = -21, the correction is found to be 0°12. 
3. Correction for Leads.—On the other hand, the water-equivalent of the coil was 
slightly over-estimated as the wires serving as leads were reckoned in, although. 
part of them protruded out of the water. The length which was outside the water 
was 2°8 centims., but about 8 millims. of this was in close contact with stout copper 
rods, the temperature of which would not rise appreciably during the experiment. 
From the previous investigation, which is applicable to this case, it would appear 
that one-third or 0:7 centim. of the part surrounded by non-conductors should have 
been taken into the water-equivalent instead of the whole. The error committed in the 
heat capacity of 2:1 centims. of copper wire, weighing ‘22 grams. per centim., that is 08, 
