Cobb and Hugh passed into the tunnel, which was brilliantly lighted by electricity, dry, and much warmer than the outer air. Moving onward, they soon came to the great chambers of the cliff. "Here, Cobb," said Hugh, as they entered the first chamber, "here are the first dynamos. This whole cliff, from the front to 1,000 feet in rear, is honeycombed with these chambers. Each chamber has a turbine wheel and a set of dynamos, and receives its water-supply through shafts drilled straight up through the roof into the waters of the rapids above. The water, after working the turbines, is discharged into the great tunnels which you saw emptying from the face of the rock. Of the mighty body of water flowing over the falls, only a portion could be used in this manner, as it was not deemed wise to make more than two rows of tunnels; but to gain as much power from the water as possible, the two lines of dynamo houses along the banks, which you saw from above, were constructed. The little tunnels are for air circulation, and fans are continually moving the air through the whole labyrinth of chambers. There are, in the face of this rock, 200 tunnels, in two rows of one hundred each, and extending back 1,000 feet, or forty miles in total length. Over each tunnel are chambers, twelve by twenty feet, with ten-foot walls between, or thirty chambers along the line of each tunnel. "Each chamber has a fifteen-inch shaft tapping the water-supply above. Now, the descent of the water is at the rate of 3,840 feet per minute, the fall is sixty feet, and the weight of a cubic foot of water 62.5 pounds: thus the horse-power of each shaft is exactly 400, and the flow-off, in area, one square foot. As there are thirty of these chambers to each discharge tunnel, then an area of thirty square feet flows from a seventy-eight-square-foot escape. But the volume of water from the shafts, owing to its increased velocity, would soon overflow the discharge tunnels if level; to obviate this, they are inclined as much as possible. Four hundred horse-power turbines in each chamber, coupled to dynamos, give 350 electrical horses. As there are 6,000 chambers in the rock, the output, in electricity, is equivalent to 2,100,000 electrical horse-power; this, added to the power generated by the fourteen miles of dynamos along the river, which have 3,650 wheels, brings the whole power utilized up to three and a quarter millions of electrical horses. This mighty current is carried by great copper cables to all parts of eastern United States, and used for every conceivable purpose where power is required." "You seem to be pretty well posted in this matter," was all Cobb could say, as Hugh gave him this array of figures. "I am. I was on a board of engineer officers in connection with the water-power of these falls, some years ago," he replied. "How long have these works been in operation?" "About fifty years." "So long?" "Yes." "Is it a private concern?" inquired Cobb.