6 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 60 



fractional decrease in the intensities of different wave-lengths found 

 by comparing them with the values which were found for them dur- 

 ing May and early June. 



Some results of the haziness are plainly shown by the accompany- 

 ing illustrations, Fig. i and Fig. 2. Fig. 1 gives the march of the 

 pyrheliometry and of the transmission of green light (at wave 

 length 0.5 fi) from June until September. It is computed for the 



Table 2. Illustrating Opacity Due to Volcanic Matter. 



Time. 



Percentage depletion. - 



Wave-lengths in microns. 



0.34 0.36 0.40 0.50 0.60 1. 00 2.00 



a. MOUNT WILSON, CALIFORNIA. 



Early June . . 

 Late June . . . 



July 



August 



Haziest days 



0.0 



0.7 

 3.4 



4-3 

 13-0 



b. BASSOUR, ALGERIA. 



Early June . . 

 Late June . . . 



July 



August 



Haziest days 



0.0 



-1.4 



6.6 



7-9 

 11. 6 



1 These values relate to pyrheliometer measurements at a solar zenith distance of 48° (air 

 mass 1.5) and mean solar distance. 



2 These values relate to atmospheric transmission for solar zenith distance of 48 (air mass 

 1.5) and depend on spectro-bolometric measurements at the wave-lengths named. The per- 

 centage depletion indicates the loss of direct radiation attributable to the volcanic haze, 

 assuming none was present in early June. 



solar zenith distance of 48 corresponding to air mass 1.5. The 

 values are given for both Mount Wilson and Bassour. In Fig. 2 

 are given the vertical transmission coefficients of the haze itself for 

 various times and wave-lengths. Curves representing this are shown 

 corresponding to the latter part of June, to July, to August, and to 

 some days when the transparency was especially low. These data 

 are also given for both Mount Wilson and Bassour. 



From these results we may draw the following conclusions : 

 (1) The haze produced by the volcano of Mount Katmai began 

 to affect measurements in Algeria on or about June 19, and those of 

 Mount Wilson on or about June 21. 



