RELATIVE EFFICIENCY OF THE TWO FALLS 445 



In contrast, the greater falls impinge on the drowned tains only after 

 they have passed through a stratum of 72 feet of water, forming a very 

 thick cushion, thus diminishing the mechanical effect of the falling water. 

 An effective descent of both falls (allowing for the acquired velocity at 

 their crests) may be taken at 180 feet. Even without knowing the sound- 

 ings, it would seem improbable that the falls could excavate in the hard 

 shales to 192 feet, as found farther down the gorge, or to a depth beneath 

 the surface of the river greater than the height of the falls. This was 

 rendered still further unlikely by the fact that in the deep channel the 

 hard Medina sandstones had also been penetrated, while now the sound- 

 ings show that the present descent of the falling water does not penetrate 

 them.^^ Thus while the full efficiency of the American Falls is at work 

 on the exposed rocks and talus masses, a third, or perhaps more, of the 

 effective force of the great mass of water of the Canadian Falls is lost in 

 friction, heat, and the counterbalancing hydrostatic pressure of the river. 



While there is still some current when the falls reach the talus at a 

 depth of 72 feet, yet it is broken up on the talus, just as is seen above the 

 river surface below the American Falls, and it soon loses its greater me- 

 chanical effect among the fallen blocks ; but the chemical solution by the 

 circulating currents, which can no longer shift the blocks, is most active ; 

 else the talus heap would grow so as to produce rapids in place of falls. 

 Such results may be seen at some small cataracts. 



Some unfinished experiments of falling water in which I had the op- 

 portunity of taking part led me to conclude that when the descent is like 

 that of a rapid, a gentle current may reach to a considerable depth, slowly 

 moving fine particles, as in the deeper holes of a stream where alluvium 

 is being deposited; but when the descent is by a considerable fall into a 

 basin, the blow is so checked that the current capable of moving fine sand 

 reaches approximately to only two-thirds of the descent of the fall above 

 the surface of the basin. The experiments were made on already loose 

 materials, and it seems to me that the relative result would be further 

 reduced where the force of abrasion is applied to solid rocks. 



Observations and measurements made in determining the efficiency of 

 a water power where the water descends 208 feet in a penstock of 3 feet 

 diameter, having an inclined position, gave the gross amount of work as 

 1,631 horsepower, while the relative efficienc^^ when using the full volume 

 of water was 78.5 per cent; but when using only from 90 to 67 per 

 cent of the water it actually rose to 80 per cent, thus showing greater 

 power where there was some freedom in the tube. Usin^ 50 per cent of 

 the water, the efficiency fell only to 76 per cent, or 2^ below that of the 

 greatest power. The use of 40 per cent yielded 70; 30 per cent brought 



Op. clt, pp. 56-58. 



