NO. 29 VOLCANOES AND CLIMATE ABBOT AND FOWLE 13 



Direct solar beam 1.250 cal. per sq. cm. per min. 



Total sky radiation 0.245 " " " " " " 



Absorbed radiation 0.175 " " " " " " 



Sum 1.67 " " " " " " 



Solar constant 1.95 " " " " " " 



DifYerence 0.28 " " " " " " 



The difference between the solar constant and the sum of the 

 three parts of the solar radiation, received at the earth's surface or 

 absorbed in the lower atmosphere, gives approximately the combined 

 loss by diffuse reflection from the atmosphere to space and by 

 absorption in the higher atmosphere. This quantity is about 0.28 

 calories per square centimeter per minute. Experiments of similar 

 nature have been made at Mount Wilson and Mount Whitney in 

 former years, and their result has always indicated that the com- 

 bined higher atmospheric absorption and the reflection of the atmos- 

 phere to space was not more than about 0.05 calories per square 

 centimeter per minute. Accordingly the difference of 0.20 calories 

 in round numbers seems to be attributable to the uncommon haziness 

 which prevailed in the higher atmosphere during the summer of 

 1912. This difference is about 10 per cent of the solar constant of 

 radiation. 



It might be expected that if so great a decrease as this in the 

 heat available to warm the earth's surface should continue indefi- 

 nitely, the mean temperatures recorded at meteorological stations 

 would thereby be lowered by about J° centigrade. But it is not 

 certain that the effect of this considerable diminution of heat was 

 not counteracted by some change in the average cloudiness, or in 

 the nocturnal radiation of the earth to space. It is conceivable that 

 the cloud of haze prevented the escape of radiation of the earth to 

 space in the same manner that it prevented the incoming of radia- 

 tion from the sun to the earth, so that the decrease of heat available 

 to warm the earth may have been in part or in whole compensated 

 by a decrease in the rate of escape of heat from the earth, owing to 

 the presence of the haze. 



Mr. Angstrom has kindly communicated to us some measurements 

 of the nocturnal radiation which he made at Bassour in the summer 

 of 19 1 2. Unfortunately these measurements were not begun until 

 after the haze from the volcano had reached a considerable density, 

 but Mr. Angstrom has arranged his values with reference to the 

 degree of haziness which prevailed, as indicated by pyrheliometric 

 measurements of the direct beam of the sun during the successive 



