For a time the experimenters with the transmission of electricity along a wire were on the wrong track. They were experimenting with a continuous current which, as we have seen, is produced from an ordinary dynamo with the aid of a commutator. But hosts of experiments finally made it clear that this form of current, no matter how powerful it might be, is unable to traverse considerable distance without great loss, being frittered away in the form of heat. But the very term "continuous current" implies the existence of a current that is not continuous. In point of fact, we have already seen that a dynamo, if not supplied with a commutator, will produce what is called an alternating current, and such a current has long been known to possess properties peculiar to itself. It is, in effect, an interrupted current, and it is sometimes spoken of as if it really consisted of an alternation of currents which move first in one direction and then in another. Such a conception is not really justifiable. The more plausible explanation is that the alternating current is one in which the electrons are not evenly distributed and move with irregular motion. Perhaps we may think of the individual electrons of such a current as oscillating in their flight, and, as it were, boring their way into the resisting medium. In any event, experience shows that such a current, under proper conditions, may be able to traverse a conducting wire for a long distance with relatively small loss. It must be understood, however, that the mere fact that a current alternates is not in itself sufficient to make feasible its transmission to a remote distance. To meet all the requirements a current must be of very high voltage. This means, in so far as we can represent the conditions of one form of energy in the terms of another, that it shall be under high pressure. Fortunately a relatively simple apparatus enables the electrician to transform a current from low to high voltage without difficulty. And so at last the problem of transmitting power to a distance of many miles has been solved. Electrical currents representing thousands of horse-power are to-day transmitted from Niagara Falls to the city of Buffalo over ordinary wires, with a loss that is relatively insignificant. A plant is in process of construction that will similarly transmit the power to Toronto; and it is predicted that in the near future the powers of Niagara will be drawn upon by the factories of cities even as far distant as New York and Chicago. Practical difficulties still stand in the way of such very distant transmission, to be sure, but these are matters of detail, and are almost certain to be overcome in the near future.