2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 



VII. There is no evidence of maxima or minima of atmospheric 

 radiation during the night that cannot be explained by 

 the influence of temperature and humidity conditions. 

 VIII. There are indications that the radiation during the daytime is 

 subject to the same laws that hold for the radiation during 

 the night-time. 

 IX. An increase in altitude causes a decrease or an increase in the 

 value of the effective radiation of a blackened body 

 toward the sky, dependent upon the value of the tempera- 

 ture gradient and of the humidity gradient of the atmos- 

 phere. At about 3,000 meters altitude of the radiating 

 body the effective radiation generally has a maximum. 

 An increase of the humidity or a decrease of the tempera- 

 ture gradient of the atmosphere tends to shift this maxi- 

 mum to higher altitudes. 

 X. The effect of clouds is very variable. Low and dense cloud 

 banks cut down the outgoing effective radiation of a 

 blackened surface to about 0.015 calorie per cm. 2 per 

 minute ; in the case of high and thin clouds the radiation 

 is reduced by only 10 to 20 per cent. 

 XL The effect of haze upon the effective radiation to the sky is 

 almost inappreciable when no clouds or real fog are 

 formed. Observations in Algeria in 1912 and in Cali- 

 fornia in 1 91 3 show that the great atmospheric disturb- 

 ance caused by the eruption of Mount Katmai in Alaska, 

 in the former year, can only have reduced the nocturnal 

 radiation by less than 3.0 per cent. 



XII. Conclusions are drawn in regard to the radiation from large 

 water surfaces, and the probability is indicated that this 

 radiation is almost constant at different temperatures, and 

 consequently in different latitudes also. 



