On Sun-heat and Radiation. 97. 
The foregoing Table is constructed on the supposition that equal 
quantities of sun-heat are absorbed by the atmosphere at all zenith 
distances ; but, although this supposition is only a first approxi- 
mation, yet by comparing the total quantities of sun-heat at each 
latitude with the following Table of Mean Annual Temperatures, 
some valuable conclusions may be drawn relative to the absolute 
radiation of heat into space from the earth’s surface regarded as a 
whole. 
Mean ANNUAL TEMPERATURES. * 
sent Temperature. anaes Temperature. 
° 3 - ‘ 
0 80-1 F. 0 eit E 
10 18:7 y 10 81-0 
20 Ah 3 20 176 ,, 
30 66-7 ,, 30 67°6 ,, 
40 579 ,, 40 5655 , 
50 478 ,, 50 43-4 
60 35°3 ,, 60 29-3 ,, 
70 14-4 ,, 
80 43 ,, 
Let 
7 =annual sun-heat at a given latitude measured in feet of ice ; 
@= mean annual temperature of a given latitude ; 
k=an unknown coefiicient ; 
# =unknown radiation into space at that latitude. 
Assuming that 6, the mean annual temperature of a given 
parallel of latitude, is proportional to the heat retained, we have— 
T =total heat received ; 
k@ = heat retained ; 
fF =heat lost by radiation ; 
and, therefore, . 
T=k0+R. . 
* W. Ferrel, United States Coast Survey. ‘‘ Meteorological Researches,” Part I., 1877. 
’ Sc1EN, Proc. R.D.S., Vou.11. Pt, 1. H 
