FOE DETEEMINING- THE EADIATIHO POWEES OF SUEFACES IN AIE. 401 
Series of 
experiments. 
Values of 9 (C.). 
Values of t (C.). 
Calculated 
values of Q. 
Observed 
values of Q. 
Differences. 
I. 
l§-6 
4^7 
1-56 
1-52 
0-04 
II. 
17-6 
102-1 
4-09 
4-16 
-0-07 
III. 
16-6 
175-4 
8-95 
8-88 
0-07 
The small amount of the cliiFerences registered in the last column are sufficient to 
indicate the very approximate accuracy of the formula for at least a considerable range 
of temperature, as indicated by the values of t in the third column. 
15. I now proceed to detail three other series of experiments similar to the above, 
with a disc of Chalk made as dry as possible. 
IV. Disc of Dry Chalk. 
Duration of each experiment = 1000 beats. 
Height of the barometer . . = 30 '33 inches. 
= -77 metre. 
Number of 
experiment. 
Temperature of the 
radiating surface. 
Keadings of the 
calorimeter. 
Difference of the 
readings =R 2 — Ej. 
Temperature 
of the air. 
(1) 
T= 135-2 
/Ri = 57-92'l 
1R2= 60-57/ 
2-65 
60-5 
(2) 
T=135-6 
rRj = 58-95'l 
1R2=61-6 o/ 
2-65 
(3) 
T=135-6 
/R. = 59*521 
\R2=62-17/ 
2-65 
61 
(4) 
T= 135-5 
/ Ri=59-28l 
1R2=61-99/ 
2-71 
61 
(5) 
T= 136-4 
/Ri= 59-251 
1R2=61-76/ 
2-51 
61-5 
Hence, adopting the same notation as above for the mean values, we have 
(T)=135°-66 (F.), 
(E)= 60°-30 (F.)=15°-7 (C.)=^, 
(T)-(R)= 75°-36 =4r-66 (C.)=^. 
Also, taking the mean of the “ Differences,” 
Eg— El =2*66 for 1000 beats, 
=1-33 for 600 beats. 
3 H 
MDCCCLX. 
