672 Proceedings of the Royal Soeiety 
diameters, being J inch, 2 inches, and 4 inches respectively. 
These boxes were provided with an opening in the centre of one 
end, for the purpose of introducing a thermometer to determine 
their temperatures. Before being used they were painted black, to 
get a good and a uniform condition of all the absorbing surfaces. 
After a thermometer was fitted into each box, they were all 
hung up under the horizontal shade, and perfectly protected from 
the direct rays of the sun. Alongside of the boxes was hung a 
thermometer with a clean bulb, also a thermometer having the bulb 
blackened with the same paint as used for the boxes. After they 
had hung for some time, no two of the boxes were found to have 
the same temperature. The larger the box the higher was its 
temperature. The difference between the temperatures, as might 
be expected, was not always the same, because on no two days is 
the amount of radiant heat the same, nor is the rate of circulation 
of the air the same. The following table shows the readings taken 
at two different times on the same day ; — 
Clean Bulb. 
Blackened 
Bulb 
diameter. 
Box 
diameter. 
Box 
2" diameter. 
Box 
4" diameter. 
67° 
68° 
69°-5 
71°-3 
74°-l 
71 ° 
72° 
74° -2 
76° 
79° 
These readings, of course, only show the comparative tempera- 
tures at the particular place on the day the observations were 
made. Some days the difference was less, but in spring weather, 
wdien the sun is hot and the air cold, greater differences may be 
looked for. 
The boxes with their thermometers were then hung up under the 
horizontal sunshade in an open field, clear of all buildings, and 
surrounded by trees at some distance. The amount to which the 
different boxes were heated was found to be almost the same as in 
the more confined place, where the tests were first made ; showing 
that the amount of heating is not much influenced by the nature of 
the surrounding objects. 
The above readings were shade temperatures ; the boxes were now 
