FOE DETEElVimNG THE EAHIATIHG POWEES OF SHEFACES IN AIE. 407 
calorimeter. Hence the heat communicated to the calorimeter in each experiment may 
be considered to have been employed in raising by the observed amount in the observed 
time the temperature of 5689’5 grains of distilled water. Taking 1000 grains as the 
unit of weight, this weight will be represented by the number 5-6895. 
Again, the time corresponding to 500 beats of the watch employed (the time to which 
all the experimental results were reduced) v/as =3-3333 minutes. Now the above 
quantity of water was raised Q® in that time, or 
OP 
3-3333 
in one minute, which we may take 
as the unit of time. Consequently the heat would have raised a unit of water (1000 grs.) 
QO 
———.5-6895 degrees in one minute; or if Q’ denote the numerical value of the heat 
3*3333 
communicated to the calorimeter with the thermal unit above mentioned, we have 
5:6895 
^ 3-3333 
=1-706 0''. 
Also the area of the radiating surfaces was 23-758 square inches, and therefore if Q 
denote the quantity of heat emanating from a square foot, 
144 
- ^- 758 ’ 
Q'=6-060; 
or finally. 
0=10-338 0“. 
Hence in each of the preceding expressions for O®, we must multiply the numerical 
factor of each term by 10-338, and we shall obtain the numerical value of the quantity 
of heat which would emanate in one minute from a square foot of the proposed surface 
for any assigned value of the temperature denoted by 6 (Cent.), and the difference of 
temperatures denoted by t (Cent.), the unit of heat being that heat which would raise the 
temperature of 1000 grains of distilled water 1° (Cent.). Our formulae thus become for 
Glass. 
Q=9-566«V-1)+-03720 
Dry Chalk. 
Q=8-613aV-l)+-03720 (.■^) 
Dry New Bed Sandstone. 
Q=8-377aV-l)4-'03720 (.f^) 
