207 
of Edinburgh, Session 1869-70. 
the corner of the diagram, where the dotted lines belong to one 
day’s experiments, and the double lines to those of another day. 
The numbers (H) given in the following table, which is formed 
from means of many experiments, and which is shown graphically in 
the diagram, express in grains the quantity of water which would 
be heated 1° Centigrade by the heat lost (by radiation and con- 
vection jointly) by one square inch of surface in an hour, its 
temperature being kept constant. With the apparatus employed, 
it was not easy to keep the pressure lower than 10 mm ; but the 
curves for different pressures show that in this case the convection 
must be small, so that (roughly) we may take the numbers given 
for that pressure as representing the radiation alone. 
Blackened. Bright. 
Pressure. 
Temperature C. 
H. 
Temperature C. 
H. 
760 mm 
61*2 
6258 
63*8 
3537 
50-2 
4875 
57T 
3091 
4T6 
3867 
50*5 
2637 
34*4 
3082 
44-8 
2251 
27-3 
2294 
40-5 
2013 
20 ’5 
1629 
34-2 
1571 
29*6 
1353 
23*3 
996 
18-6 
751 
102 mm 
62-5 
4650 
67-8 
1763 
57 -5 
4150 
61*1 
1552 
53-2 
3760 
55* 
1371 
47-5 
3220 
49-7 
1220 
43* 
2835 
44-9 
1082 
28-5 
1755 
40-8 
960 
10 mm 
62-5 
4236 
65 - 
1390 
57-5 
3847 
60* 
1273 
54*2 
3593 
50- 
1025 
41*7 
2600 
40- 
786 
37*5 
2292 
30- 
563 
34* 
2040 
23-5 
445 
27-5 
1600 
24' 2 
1400 
