12 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



the values at different latitudes are as given in table 6 for clear skies. 

 For half-cloudy skies we take the mean of the two conditions. 



We are now prepared to assemble our results and compare them 

 with those of Simpson (table 7). 



It is clear that our employment to a considerable extent of inde- 

 pendent data and methods has made no very great difference in the 

 totals from those of Simpson. The range of our totals for half- 

 cloudy sky is indeed considerably greater than his as between the 

 equator and the poles. Our method has enabled us to segregate the 

 contributions of the atmosphere and of the earth's surface, which 

 in Simpson's second paper are not computed separately. We find the 

 earth's surface almost equally contributing at all latitudes, but the 



Table 7. 



-Radiation of Earth and Atmosphere to Space 

 Calories per cm.^ per min. 



Latitude 



Smithsonian results 



Clear sky 



Atmos- 

 phere 



Sur- 

 face 



Total 



Half -cloudy sky 



Atmos- 

 phere 



Surface 

 or cloud 



Total 



Simpson results 



Atmosphere plus surface 



Clear 



Over- 

 cast 



Half- 

 cloudy 



O 

 40° 

 50° 

 60° 

 70° 

 90° 



0.220 

 0.192 

 0.182 

 0.162 

 O.151 

 0.129 



0.105 

 0.107 

 0.105 

 0.104 



O.I 00 



0.096 



0.325 

 0.299 

 0.287 

 0.266 

 0.251 

 0.225 



0.186 

 O.I7I 

 0.166 

 0.156 

 O.I5I 

 0.140 



0.102 

 0.103 

 0.102 

 0.102 



O.I 00 

 0.098 



0.288 

 0.274 

 0.268 



0.258 



0.251 

 0.238 



0.316 

 0.307 



0.291 



0.274 

 0.253 



0.213 

 0.243 

 0.249 

 0.252 

 0.253 



0.264 



0.275 



0.270 



0.265 

 0.253 

 0.245 



atmosphere, which contributes much more than half the total (even 

 more than two-thirds the total on cloudless days at the equator) emits 

 very much lesser proportions as we approach the poles. The two 

 sources are very dift'erent as regards wave lengths of principal contri- 

 bution ; the atmosphere emitting mostly in the region exceeding 16/1. 

 in wave length, the surface emitting principally in the region 9/u, to 13/A. 

 If we sum up the results in the seventh and tenth columns, which 

 represent our own and Simpson's totals for half-cloudy sky, and as- 

 sign weights to them proportional to the areas of earth which they 

 respectively represent, we find that the earth as a planet radiates aver- 

 ages of 0.277 or 0.265 cal. per square centimeter per minute according 

 as our results or Simpson's are taken. If we compute the same quan- 

 tity from the solar constant, 1.94 cal., and Aldrich's albedo, 43 per 



cent, the result is-^^ x 0.57 = 0.276 cal. The discrepancies are very 

 4 



small and far within the probable error of the determinations. 



I 



