Page:The Journal of geology (IA journalofgeology21894univers).pdf/341
tions and as to their capacity for sustaining a load, the current with the greater velocity would be able to remove ten units of sediments, while the slower current would remove one. Multiplying the fraction expressing the ratios between the cross sections of the two currents (1/1000000) by the fraction expressing the ratio between their velocities (1/10), we obtain a fraction which expresses their relative carrying power, if their capacities for sustaining a load were the same. This fraction is 1/10000000. If every cubic foot of air in the atmosphere held in suspension as much of sediments as every cubic foot of water in the Mississippi, then the atmosphere would have the power to transport in a given time ten million times the quantity of material transported in the same time by the Mississippi river.
With regard to the capacity for holding solid particles in suspension the air is, however, greatly inferior to water. It is evident that the load which can be carried by the air at ordinary and even in high velocities, is a great deal smaller than that which can be carried by water. The capacity in this respect of any current depends on chiefly three factors: (1) the density of the medium, (2) its velocity, and (3) its viscosity. As to the comparative densities of the two fluids, the air is only 1/813 times as heavy as water. Another circumstance also comes into consideration. When the particles of a material like quartz are suspended in water, they lose about 10/26 of their weight in the air, and the force with which they make their way downwards through the water is thus reduced to 16/26 of what it would be in the air. This still more increases the relative carrying power of water making it 1321 times as great as that of the air (813(26/16)=1321). On account of the greater average velocity of the atmosphere and also by reason of the consequent greater magnitude of its convection currents, this again has the advantage over water. But exactly to what extent these considerations affect the comparison, data are not at hand to determine. It would appear that the advantage connected with these greater convection currents more than outweighs the disadvantage due to the less viscosity of air, when compared with water. At such low