BY JAMES TOLSON, ESQ. 67 
contact with cold air. A vertical plane one foot high is found by 
experiment to lose ‘5945 unit per square foot per hour when 
heated 1° above the air in contact with it, but a high plane or wall 
loses /ess per square foot for the following reason :—Let fig. 3 
(plate II.) represent a plane 4 feet high, heated to 60° while the 
air in contact with it isat 59°. The air in immediate contact with 
the wall being heated by it, is expanded thereby, becomes lighter 
than the surrounding air and ascends in a constant current as 
shown by the arrows.’’—Box, op. cit. 
‘‘Now for the first or lowest foot, the air is at 59° to begin with, 
but departs from it at a slightly increased temperature, so that 
there is Jess than 1° difference when it comes in contact with the 
second foot, and for that reason it receives less heat from it than 
it did from the lowest foot, and so throughout each successive 
foot receives the air at progressively increased temperature, and 
imparts less and less heat to it.” 
“The loss by a vertical plane is given by the rule— 
A= "300 x (233 = 4/ EH.) 
in? which A = the loss in units per square foot per hour for 1° 
difference in temperature, and H = the height of the plane or 
wall in feet.’’—Box, op. cit. 
The following table has been calculated by this rule :— 
Table 4.—Showing the value of A, or the loss of heat by contact 
of cold air from a vertical plane of any material, with 1° 
difference in temperature between the body and the air in 
contact with it. In units per square foot per hour. 
VALUE oF A FOR VERTICAL PLANES. 
Loss of Heat || Loss of Heat 
Height of | in Units per Height of | in Units per 
the Plane Square Foot |) the Plane Square Foot 
in Feet. for 1° || in Feet. for 1° 
ditference. | difference. 
| | 
| . . 
I 5945 || 9 4386 
2 75820 |, IO "4347 
‘ 3 "4962 II "4313 
4 A7sOr Vie R12 "4283 
5 "4655 20 "4133 
6 "4561 30 "4037 
i "4491 | 40 "3980 
8 ‘4434 | + 60 "3924 
