Meanwhile, it may be understood that the mutual relations of the magnetic and electrical forces just referred to are not at all dependent upon the manner in which the electric current is generated. The magneto-electric motor may be operated as well with a chemical battery as with such a mechanical generating dynamo as has just been described. The storage-batteries which have been employed in some street railways and those which propel the electric cabs about our city streets furnish cases in point. The only reason these are not more generally employed is that the storage battery has not yet been perfected so that it can produce a large supply of electricity in proportion to its weight, and produce it economically. X NIAGARA IN HARNESS "Harnessing Niagara"--the phrase has been a commonplace for a generation; but until very recently indeed it was nothing more than a phrase. Almost since the time when the Falls were first viewed by a white man the idea of utilizing their powers has been dreamed of. But until our own day--until the last decade--science had not shown a way in which the great current could be economically shackled. A few puny mill-wheels have indeed revolved for thirty years or so, but these were of no greater significance than the thousands of others driven by mountain streams or by the currents of ordinary rivers. But about a decade ago the engineering skill of the world was placed in commission, and to-day Niagara is fairly in harness. If you have ever seen Niagara--and who has not seen it?-you must have been struck with the metamorphosis that comes over the stream about half a mile above the falls. Above this point the river flows with a smooth sluggish current. Only fifteen feet have the waters sunk in their placid flowing since they left Lake Erie. But now in the course of half a mile they are pitched down more than two hundred feet. If you follow the stream toward this decline you shall see it undergo a marvelous change. Of a sudden the placid waters seem to feel the beckoning of a new impulse. Caught with the witchery of a new motion, they go swirling ahead with unwonted lilt and plunge, calling out with ribald voices that come to the ear in an inchoate chorus of strident, high-pitched murmurings. Each wavelet seems eager to hurry on to the full fruition of the cataract. It lashes with angry foam each chance obstruction, and gurgles its disapproval in ever-changing measures. Even to the most thoughtless observer the mighty current thus unchained attests the sublimity of almost irresistible power. Could a mighty mill-wheel be adjusted in that dizzy current, what labors might it not perform? Five million tons of water rush down this decline each hour, we are told; and the force that thus goes to waste is as if three million unbridled horses exhausted their strength in ceaseless plunging. This estimate may be only a guess, but it matters not whether it be high or low; all estimates are futile, all comparisons inadequate