NO. 3 RADIATION OF THE ATMOSPHERE ANGSTROM 8l 



able cause of this remarkable haziness. As regards the atmospheric 

 conditions at Bassour, I may quote the description given by Abbot 

 and Fowle in their interesting paper, Volcanoes and Climate : " On 

 June 19 Mr. Abbot began to notice in Bassour streaks resembling 

 smoke lying along the horizon, as if there were a forest fire in the 

 neighborhood of the station. These streaks continued all summer, 

 and were very marked before sunrise and after sunset, covering 

 the sky towards the sun nearly to the zenith. After a few days 

 the sky became mottled, especially near the sun. The appearance 

 was like that of the so-called mackerel sky, although there were 

 absolutely no clouds. In the months of July, August, and so long 

 as the expedition remained in September, the sky was very hazy, and 

 it was found that the intensity of the radiation of the sun was greatly 

 decreased by uncommonly great haziness." Abbot and Dorno x both 

 agree as to the average decrease per cent in the solar radiation caused 

 by the dust ; it was found to be about 20 per cent. " In the ultra-violet 

 and visible spectrum the effect was almost uniform for all wave 

 lengths, but was somewhat less in the infra-red." (Volcanoes and 

 Climate.) 



It is of very great interest to consider, in connection with the 

 observations named, the effect of volcanic dust upon the nocturnal 

 radiation. Unfortunately the observations at Algeria were not begun 

 until after the haze had reached a considerable density, and therefore 

 we cannot compare observations taken at the same place before 

 and during the dust period. But the observations taken at Lone Pine 

 during the California expedition may furnish a reliable basis for 

 comparison, the two stations having almost exactly the same altitude. 

 If we therefore consider the curve giving the relation between radia- 

 tion and humidity at Lone Pine in comparison with the same curve 

 obtained at Bassour, both curves reduced to the same temperature, 

 we may from this draw some conclusions in regard to the effect of 

 the volcanic haze. These curves are given in figure 5, and we can 

 from the diagram read off the departures of the Lone Pine curve 

 from the curve taken at Bassour. These departures are given in 

 the following table, together with the mean departure, which is found 

 to be +0.003 or J us t about 2 per cent of the mean radiation. The 

 Lone Pine values are, on an average, a little less than 2 per cent higher 

 than the values obtained at Bassour under identical conditions. If 

 we compare the radiation values at Indio with those at Bassour in 

 the same way, we shall find a departure of +-J per cent in favor of 



3 Met. Zt., 29, 1912. 



