The wind was blowing at the rate of about fifteen miles an hour, and nearly dead fair; the engines were therefore set so as just to turn round and no more; this gave the ship a speed of about twelve knots through the air, which, added to the rate of the wind, gave a total speed of twenty-seven knots over the ground--or rather over, the water-- and at this pace they calculated that, after making the necessary allowance in their course for the set of the wind, they would reach the Irish coast, in the vicinity of Cape Clear, at about five o'clock the next morning. Their reason for not travelling faster was that, as the baronet said, they were on a pleasure cruise, and having been pent up inside the hull for fully thirty-six hours, they felt that a few hours in the open air would be an acceptable change. They pursued their flight throughout the day at an altitude of only a thousand feet above the sea, except when they encountered a ship--which happened only once during the hours of daylight--and when this occurred they rose, on the instant of sighting her, to the highest attainable distance, in pursuance of their resolve to attract as little attention as possible, descending again to their former level as soon as they had passed beyond her range of vision. At this latter elevation they were able to enjoy to the full the health-giving properties of the pure sea- breeze, and to revel in a prospect--though it was only that of the restless sea--of nearly forty nautical miles on every side; the horizon, that is to say, forming a circle of little less than eighty miles diameter round about them. And though it may be hastily thought that, with a sea bare of craft there was little or nothing to interest the travellers, this was by no means the case; for at their height the water was clear and transparent for a long distance below the surface, and the gambols of the fish, of which there were great numbers visible, including several schools of porpoises and a solitary whale, could be seen distinctly, affording a most interesting sight; and when they grew tired of this they promenaded the spacious deck, or lounged about in chairs, smoking their cigars or pipes, and discussing with much animation their future prospects. And now, for the first time, a fact in connection with the automatic balancing apparatus brought itself under their notice. It was this. They found that, let them walk about the ship where and as much as they chose, the balance of the ship always remained perfect; but the little jets of air which, at their every movement, were admitted into the hull to maintain its equilibrium, soon had a perceptible influence on the vessel's buoyancy, causing her to slowly but steadily descend toward the surface of the sea, thus necessitating periodic visits to the pilot-house to renew the vacuum. This set the professor's brain to work, and by nightfall he succeeded-- with the aid of a second barometer having a small piece of highly