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standard of comparison. Let us take, for instance, the work of transportation which is performed by the Mississippi river.

The efficiency of any transporting current is determined by three factors, viz.: (1) the area of its transverse section, (2) the velocity of its motion, and (3) its capacity for holding a load. In the case of the Mississippi basin we may say that the products of disintegration and erosion within its boundaries may be removed by principally two agents, water and air. What is removed by water all passes out through the channel of the lower Mississippi. The size of this current in transverse section is less than ⁠1/100⁠ of a square mile. It is evident that all the materials removed by this river from its great basin, whether taken from the Rocky mountains or from the Appalachian highlands, must pass through the same narrow circumscribed limits of ⁠1/100⁠ of a square mile in the lower course of the river. Now, the atmosphere may also be regarded as a current. The width of this current will be the average width of the entire drainage basin of the Mississippi, and in its height this current equals the height of the atmosphere. Taking this to be ten miles, which cannot very well be too much, and taking the average width of the Mississippi basin as one thousand miles—it is at least one hundred miles more—the transverse section of the atmospheric current will be ten thousand square miles. The ratio of the sizes of these two currents as shown in their sections is thus 1:1,000,000, i. e., the cross section of the Mississippi current is ⁠1/1000000⁠ of that of the atmosphere. If velocity and capacity for carrying a load were the same in both currents, the relative transporting power of the greater one would be 1,000,000 times that of the smaller.

In respect to velocity the Mississippi is also less effective in its work than the atmosphere above it. The average velocity of the wind over the interior basin is not less than eight miles per hour, while the average velocity of the lower Mississippi is about .7 mile per hour. The ratio of the velocities is therefore represented by the fraction ⁠7/80⁠, which is a little less than ⁠1/10⁠. If, therefore, the two currents were equal as to their cross sec-