BRIGGS AND BELZ: INFLUENCE OF HAZE 



385 



below normal, which would account at least in part for the dimin- 

 ished evaporation. May was normal, both with respect to evap- 

 oration and hours of sunshine. The evaporation for the first half 

 of June, during which the eruption of Mt. Katmai occurred, was 

 8 per cent below nonnal; the second half of June was 14 per cent 

 below normal; July, 6 per cent below; August, 8 per cent below; 

 and September, 15 per cent below. The number of hours of sun- 

 shine was also somewhat below normal during this period. The 

 Weather Bureau sunshine records are obtained with the Marvin 

 sunshine recorder, which is essentially a differential thermometer 

 in vacuo, one bulb being blackened. When the rate, at which 

 solar radiation is received, is sufficient to develop a certain differ- 

 ence in the temperature of the bulbs, the sun is recorded as shin- 

 ing. It is evident that any reduction in the intensity of the solar 

 radiation in midsummer (due to dust in the atmosphere or other 



TABLE IV 



causes) would enter into the records from this instrument as a 

 reduction in the number of hours of sunshine. The observed 

 reduction in sunshine (Table IV) following the eruption may 

 therefore be attributed, in part at least, to a reduction in the in- 

 tensity of the solar radiation transmitted by the upper atmos- 

 phere, rather than to an actual increase in cloudiness. There 

 is obviously no way of separating these two factors from a con- 

 sideration of the sunshine records alone. 



It thus appears that the average evaporation as measured at 

 15 stations was below normal during the four months following 

 the eruption of Mt. Katmai, the average reduction in evaporation 

 being about 10 per cent. This "is somewhat less than the ob- 

 served reduction in the intensity of solar radiation as reported 



