For within these walls, by a miracle of modern science, the potential energy which resides in the water of the canal is transformed into an electrical current which is sent out over a network of wires to distant cities to perform a thousand necromantic tasks,--propelling a street car in one place, effecting chemical decompositions in another; turning the wheels of a factory here and lighting the streets of a city there; in short, subserving the practical needs of man in devious and wonderful ways. Even as you gazed disdainfully at the stagnant canal, its waters, miraculously transformed, were propelling the trolley cars along the brink of the cliff over there on the Canadian shore, and at the same time were turning the wheels in many a factory in the distant city of Buffalo. After all, then, the quiet pool of water was not so prosaic as it seemed. As you stand in the building where this wonderful transformation of power is effected, the noble simplicity of the vista heightens the mystery. The most significant thing that strikes the eye is a row of great mushroom-like affairs, for all the world like giant tops, that stand spinning--and spinning. These great tops are about a dozen feet in diameter. They are whirling, so we are told, at a rate of two hundred and fifty revolutions per minute. Hour after hour they spin on, never varying in speed, never faltering; day and night are alike to them, and one day is like another. They are as ceaselessly active, as unwearying as Niagara itself, whose power they symbolize; and, like the great Falls, they murmur exultingly as they work. [Illustration: VIEW IN ONE OF THE POWER HOUSES AT NIAGARA. Each of the top-like dynamos generates 5000 horse-power.] The giant tops which thus seem to bid defiance to the laws of motion are in reality electric dynamos, no different in principle from the electric generators with which some visit to a street-car power-house has doubtless made you familiar. The anomalous feature of these dynamos--in addition to their size--is found in the fact that they revolve on a vertical shaft which extends down into a hole in the earth for more than a hundred feet, and at the other end of which is adjusted a gigantic turbine water-wheel. Water from the canal is supplied this great turbine wheel through a steel tube or penstock, seven feet in diameter. As the turbine revolves under stress of this mighty column of water, the long shaft revolves with it, thus turning the electric generator at the other end of the shaft--the generator at which we are looking, and which we have likened to a giant top--without the interposition of any form of gearing whatever.