6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



As a second step, we consider the spectral distribution and intensity 

 of emission of the perfect radiator at different temperatures/ By- 

 interpolation on large scale plots we have prepared table 3. This gives 

 the approximate' intensity of emission of the perfect radiator at tem- 

 peratures corresponding to the mean temperatures of Simpson's lay- 

 ers, and to those of his selected latitudes of the earth's surface. 



Multiplying the values in table 2 by corresponding ones in table 3, 

 we obtain the emission of radiation outwards from each Simpson at- 

 mospheric layer towards a complete hemisphere. The values are given 

 in table 4. 



Again interpolating in the plots (fig. 3) we next obtained the trans- 

 mission coefficients for each superincumbent atmospheric mass lying 

 above the respective Simpson layers. Allowance is made for the ozone 

 absorption between gix and iifi. These values are given in table 5. 



Multiplying these values by corresponding ones in tables 3 and 4, 

 We obtained the contributions of the Simpson atmospheric layers and 

 also of the earth's surface' at the latitudes 90°, 70°, 60°, 50°, 40°, 

 and 0° to the intensity of emission of the earth as a planet towards 

 outer space."* These results are given in table 6. 



All of these results apply to cloudless skies. We now assume, with 

 Simpson, that the earth is 50 per cent cloudy ; that the clouds totally 

 absorb all radiation arising from beneath them ; that they radiate quite 

 as efficiently as the perfect radiator ; and that their upper surfaces 

 maintain the same average temperature as the earth at 70° latitude. 

 We are not able to compute their radiation in Simpson's manner, since 

 we have shown reasons to believe that the stratosphere is almost desti- 

 tute of water vapor, instead of containing 0.3 mm. of precipitable 

 water as he supposes. We simply assume that the combined emission 

 of clouds and atmosphere during one-half the time at all latitudes is 

 the same as that of the earth's surface and the superincumbent atmos- 

 phere at latitude 70°. That is: For the atmosphere 0.151 cal. per 

 crn.' per min. ; for the cloud surface o.ioo cal., giving a total for com- 

 pletely overcast sky of 0.251 cal. During the other half of the time. 



^ See Smithsonian Physical Tables, p. 248. 



' We do not guarantee these values to within 2 per cent. 



* We assume, with Simpson, that the earth's surface may be regarded as a 

 perfect radiator. 



^ Notwithstanding our previous evidence that the water-vapor content of the 

 stratosphere is vanishingly small, we have thought best to estimate 30 per 

 cent of black-body efficiency as applicable to the stratospheric radiation in the 

 wave-length region 13^ to 50,u, where water vapor is so very active. We have 

 allowed 16 per cent of black body efficiency to the ozone band, gn to ii/x. 



