ER OSION PERFORMED B V THE A TMOSPHERE. 3 2 7 



the experiment are of the most delicate kind and a slight change 

 in the velocity will cause a considerable variation in the quantity 

 of the load. 



If then the ratio of the sections of the two currents is 

 ^qqIqp^^ , the ratio of their velocities ^, and the ratio of their 

 loads per unit of bulk of the two media is I-^oajl, the ratio of 

 their respective transporting powers is as the products of these 

 fractions, or ^^. This is the same as to say, that if a cubic 

 foot of air can hold in suspension yirTinr o^ ^^^ quantity of fine 

 dust held in the same way by the water in the Mississippi river, 

 and if the velocity of the winds in the atmosphere is on the aver- 

 age not less than ten times as great as the rapidity of the current 

 in the river, and if the area of a vertical section of the atmos- 

 phere over the valley is i, 000,000 times as large as the area of a 

 cross section of the lower stream, — then the capacity of the 

 atmosphere to transport dust is 1,000 times as great as that of 

 the river. 



Atmospheric currents bemg loaded, mostly, only to the extent of an 

 insignificant fraction of their capacity, their sediments will be better 

 sorted than deposits in water-currents, which are more often loaded to 

 their fidl capacity. 



It is evident that the greater the load carried by any current, 

 the shorter is the average distance from particle to particle while 

 in transport. This increases the chances for the particles to be 

 affected by each others' movements through the medium and 

 thus for coming together to form clusters. This process, which 

 has been called flocculation, causes more rapid sedimentation; 

 for such a cluster of particles will fall faster through the medium 

 than will the separate grains of which it is composed. Floccula- 

 tion takes place among particles of all sizes, and small particles 

 which would otherwise be retained in the supporting medium, 

 will easily settle when collected into these clusters. Sediments 

 which have been formed under such circumstances will hence 

 contain a proportionally greater quantity of fine material than if 

 flocculation had not taken place. But flocculation increases with 

 the quantity of the load, and since the load of the atmosphere is 



