“But is not the power exerted to drive so great a body of air exceedingly costly?”

“No,” he answered.  “As you are aware, electricity is almost our only motive power, and we calculate that the labour of two men, even without the help of machines, could in their working zydau [eight hours] collect and reduce a sufficient amount of the elements by which the current is created to do the work of four hundred men during a whole day and night.”

“And how long,” I inquired, “has electricity had so complete a monopoly of mechanical work?”

“It was first brought into general use,” he replied, “about eight thousand years ago.  Before that, heated air supplied our principal locomotive force, as well as the power of stationary machines wherever no waterfall of sufficient energy was at hand.  For several centuries the old powers were still employed under conditions favourable to their use.  But we have found electricity so much cheaper than the cheapest of other artificial forces, so much more powerful than any supplied by Nature, that we have long discontinued the employment of any other.  Even when we obtain electricity by means of heat, we find that the gain in application more than compensates the loss in the transmutation of one force into another.”

In the course of little more than half an hour we emerged from the tunnel, whose gloom, when once the attraction of novelty was gone, was certainly unpleasant to myself, if not by any means so frightful as Eveena still found it.  There was nothing specially attractive or noticeable in the valley through which our course now ran, except the extreme height of its mountain walls, which, though not by any means perpendicular, rose to a height of some 3000 feet so suddenly that to climb their sides would have been absolutely impossible.  Only during about two hours in the middle of the day is the sun seen from the level of the stream; and it is dark in the bottom of this valley long before the mist has fallen on the plain outside.  We had presently, however, to ascend a slope of some twenty-five feet in the mile, and I was much interested in the peculiar method by which the ascent was made.  A mere ascent, not greater than that of some rapids up which American boatmen have managed to carry their barques by manual force, presented no great difficulty; but some skill is required at particular points to avoid being overturned by the rush of the water, and our vessel so careened as to afford much more excuse for Eveena’s outbreak of terror than the tunnel had done.  Had I not held her fast she must certainly have been thrown overboard, the pilot, used to the danger, having forgotten to warn us.  For the rest, in the absence of rocks, the vessel ascended more easily than a powerful steamer, if she could find sufficient depth, could make her way up the rapids of the St. Lawrence or similar streams.  We entered the second tunnel without any sign of alarm from Eveena perceptible to others; only her clinging to my hand