“I shall thank you for the privilege of inspecting the _Mystery_,” said the customs officer, whose manner now indicated respect bordering upon awe. When the two men were rowed out to the vessel a little later, there was quite a fleet of small boats hovering about her, their occupants all manifesting the greatest curiosity. Captain Penniman took his guest aboard, and they plunged at once into the mysteries below. Above decks, she was simply one of the best type of great private steam yachts. When the engine-room was reached it was not apparent to a landsman’s eye that the machinery of the _Mystery_ differed much from that of an ordinary modern steamship of her size and general type. Captain Penniman merely remarked that he did not understand himself the technic of that department. “I believe,” he said, “that much of her machinery remains just as it was originally constructed for steam. Carbonic acid gas is introduced into strong cylinders just as steam would be. It comes through an automatic valve which regulates the pressure, and puts the power of this new agent under the same control that steam was held in. They tell me that this valve which delivers just the requisite quantity of carbonic acid gas for each stroke of the piston is the invention which furnishes the key to the whole discovery. Attempts have been made for several years to utilize the tremendous expansive power of this liquified gas, but none of them succeeded until this valve was devised. I tell you, my friend, steamships will become more out of date than sailing vessels as soon as the success of this experiment is known.” “But how do you get such terrific speed?” “By using larger propellers and turning them faster. Our screws revolve at about one hundred and ten revolutions a minute, while those of the so-called crack liners make only eighty-five to ninety. We have shafts as large as those of a 12,000 ton boat, and they have stood the strain coming over without a sign of weakness. But come into the boiler-room.” Instead of the great hot fire-hole with dozens of blazing furnaces and coal heaped about, there was a small apartment, or rather two, one each side of the engine-room. The still bewildered collector saw only three long rows one above another of what were apparently copper cylinders such as are supplied to the soda-water fountains in America. He noticed, however, that each cylinder was nearly ten feet long, and from the end of each a pipe led toward the engine-room.