rOE DETEEMmmG THE EADIATING POWEES OE SUEFACES IN AIE. 405 
similar to those given in the preceding series. Calling these series VII., VIII., IX., the 
values obtained for A are 
A=:l-526 from VII. 
A= 1-608 from VIII. 
A= 1-341 from IX. 
Mean value of A= 1-459, and the general formula becomes 
Q«=l-459aV-l) + -00648(^|2)''^’''' (11-) 
Comparison of Observed and Calculated Values of Q for dry New Red Sandstone. 
Series of 
experiments. 
Values of 6 (C.). 
Values of t (C.). 
Calculated 
values of Q. 
Corrected observed 
values of Q. 
Differences. 
VII. 
16-22 
45-86 
1-44 
1-47 
0-03 
VIII. 
15-18 
87-83 
3-24 
3-29 
0-05 
IX. 
16-95 
141-57 
6-24 
6-15 
-0-09 
18. From two series of experiments (X. and XI.) on a disc of Sandstone used for 
building purposes, I obtained the following values of A : — 
A = 1-620 from series X. 
A = 1-475 from series XI. 
In X. the temperature t was = 93°-7 (C.), 
In XI. the temperature t was =151°-14 (C.). 
The mean value of A = 1-547, and our general formula becomes 
Q"=l-547«®(«'— 1) + -00648(|:|^^ (12.) 
19. Two other series of experiments (XII. and XIII.) were made in a similar manner, 
with a disc of limestone, the surface of which was highly poUsJied. 
A = 1-660 from series XII. 
A=l-613 from series XIII. 
Mean value of A= 1-586, the value of t being 
97°-65 (C.) in XII. 
155°-1 (C.)inXIIL 
The general formula becomes 
Q''=l-586aV-l)+-00648(^.-^y'^"-^^^ (13.) 
20. Two similar series (XIV. and XV.) were made with the same disc, the radiation 
taking place from its unpolished surface. The following values were obtained : — 
A=2-060 . ... t= 63-5 (C.). 
A=2-161 .... i5=125-7 (C.). 
