FOE DETEEmNIXa THE EADIATING POWEES OF SHEFACES IN AIE. 399 
(3) Correction due to the thickness of the disc . — This correction must be applied, like 
the last, to the mean values of Q derived from each of the series of experiments I., IT., 
and III. Now in 
= (F.) nearly. 
I. 
II. 
III. 
-= -6 (as in (2)). 
(F.), 
-7. 
?fi=380" (F.), 
-= - 8 . 
i\Iso we may take as a mean value of r for I., II. and III., 
r = 63° nearly. 
The thickness of the glass plate we have 
h=fQ inch, 
= •005 foot; 
and for glass, I assume 
-=l-0*; 
c 
and therefore for our glass plate the values of - are 
•008 in experiment I. 
•007 in experiment II. 
•006 in experiment III. 
Also the values of 1 — ^or of 1 — in the experiments^ become 
•6 in I. 
•75 in II. 
•83 in III. 
and the formula (4.), art. 9, becomes in 
I. Q“=l-52{l + -0048}. 
II. Q«=4-16{l + -0052}. 
III. Q'’=8-88{l+-0050}. 
(4) We have finally to take the correction investigated in art. 10. On account of it 
we must take 
Q 
* I have not determined the conducting power of glass directly by experiment. I have assumed it to be 
the same as for the most compact igneous rock, as given in my former memoir. 
