192 Mr. Powell's experimental enquiry into the nature of 
coatings employed, deduced from the observed rates of cool- 
ing, were in a ratio which happened to be almost exactly 
the inverse of that of the diameters ; but this eflect is pro- 
bably always small, and I have roughly allowed for it, as 
will be seen immediately ; taking the temperature of the 
screen by a small thermometer having its bulb in contact 
with the central part of the surface. 
II. (ii.) I now proceed to state the results, which will be 
most conveniently exhibited in a tabular form. 
1 st Set. Incandescent iron. Distance 7 inches. 
Glass screen. 
Experiment. 
Rise of Thermometer in 
I min. centigrade. 
A. White. 
B. Black. 
1 
1.25 
2.5 
2 
1.25 
fs- 
Mean 
1.25 
2.75 
Allowing for the screen 7 
(as below. 3 ^ 
2.5 
No screen. 
1 
7.5 
9.76 
2 
6.5 
7.75 
Mean 
7. 
8.75 
Difference of exposed 
and screened results. 
6.25 
