ATMOSPHERIC DUST. 



43 



was made of each catch. The maximum hourl.y velocities 

 of the wind for each day ranged from nine to twenty 

 miles. In this case also there was a correspondence be- 

 tween the wind velocities and the quantities of the dust 

 caught, but on examining the analyses, it it seen that 

 the coarse admixtures rather decrease than increase with 

 the speed of the wind. The fine ingredients are quite as 



Table XXVIf. Mechanical Composition of Dust collected directly from the Atmosphere 

 by means of Muslin, smeared with Glycerine, July, Aug. Sept., 1895. 



Lengtli of 



diameter in 



mm. 



From the flagpole 



during June and 



July, 1896. 



Under trees 

 in a grove. 



rop cloth on flag- 

 pole, Aug, 19, 

 1895. 



Bottom cloth on 



flag pole, 



Aug, 19, 1896. 



Average, 



16-8 

 8-4 

 4—2 

 2-1 



1 1 



10 

 1 _ 



1^8 



1 (i 



. 1 



aw 



. 1_ 

 r2"8 



_ 1 



tr. I 



well represented for the daj^s with high winds as for days 

 with low winds (Tab. XXVI). 



Some dust was collected at the same place and at the 

 same height by suspending two jiieces of muslin held 

 horizontally on a frame. The muslin was smeared with 

 glycerine, to which the dust adhered. This Avas secured 

 by washing and allowed to settle as before. One sam]jle 



