66 PRESERVATION OF FOOD BY REFRIGERATION ; 
Ree! _ 552 x t 1238 
t 
in which t = the difference of temperature of the body and the air 
in contact with it in degrees centigrade, and R”’ = the ratio of 
the loss of heat with that difference. 
‘Tt should be observed that the departures from the simple law 
are much less than with radiant heat. The following table gives 
the ratio of the loss of heat by contact of cold air. 
Table 3.—Showing the Ratio of Heat emitted or absorbed by 
- contact of cold air with given differences of temperature. 
Difference of Difference of 
Temperature of | Ratio || Temperature of | Ratio 
the Air andthe | of Heat. || the Air and the | of Heat. 
Body in Contact Body in Contact 
1 C: i. C. 
3.6 2 650 || 99 | 55 1.403 
5.4 3 713 |) 108 _ |) Gs 1.433 
Wee 4 702 ||. 7. is 1.460 
9 5 803 126 70 1.486 
18 10 944 || 135 75 145,00 
27 15 1.037 144 80 1-528 
36 20 TENGE 15 85 L554! 
45 25 1.169 162 go 1.575 
54 30 1.220 |||" sit 95 1.595 
63 35 1.264 || 1809 es 1.615 
V2 40 r.305. || 189 105 1.032 
81 45 1.340. ||| .LOS™ 0) aie 1.650 
go 50 e372 
“Tet P (plate Il., fig. 2) be a cube of any material, having 
its surfaces, SS, one foot square maintained at 60°, and let the 
walls, WW, also have the temperature of 60° F., while the air in 
contact with SS is at 59°. ‘There will be no loss of heat in this 
case from SS by radiation because WW and SS are at the same 
temperature, nor will there be any loss by conduction as P has the 
same temperature all through, but heat will be given out to the 
cold air, and experiment has shown that the amount for r° as in 
our case is *5945 unit per square foot per hour, for a plane one 
foot high, but it will not be the same for any other height as 
will now be shown. 
“Tf we investigate the loss of heat by a vertical plane we shall 
be able to see the reason for the variation in the loss of heat by 
