The two boys did not know the use of one quarter of the machinery and apparatus they gazed on. There were electric motors, storage batteries, two gasoline engines similar to those used in automobiles, pumps, large and small tanks, instruments for measuring the electric current, for telling the temperature, the amount of moisture in the air, the speed of the wind, the speed of the ship, the height to which it went, besides compasses, barometers, telescopes, and other instruments. There were levers and wheels on every side, switches, valves, electric plugs and handles. Lockers arranged close to the wall and along the floor held supplies and materials. Everything was new and shining, and the professor smiled with pride as he touched piece after piece of machinery, and looked at the different instruments. "Now we'll go out on the stern," he said. The boys followed as he ascended the companion steps and emerged on a small platform at the rear end of the cabin. "Do you know what this is?" asked the professor, touching a long, thin, round object. "Looks like a gun," replied Mark. "That's just what it is. It's a machine gun that will fire one hundred shots a minute, and it can be turned in any direction, as it works on a swivel. I don't know that we'll have any use for it, but I thought I'd take it along." Then the professor pointed out where the propeller shaft ran from the engine room out through the stern, and showed how the rudder was worked by wire ropes extending from it to the conning tower. "In short we have everything necessary to successfully navigate the air," he went on. "Not a thing has been overlooked. All I have to do is to fill the big bag of oiled silk with a new gas I have discovered and up we go. This is really the most important part of the invention. Without this powerful gas the airship would not rise above the earth. "But I have found this gas, which can be made in unlimited quantities from simple materials that we can carry with us. The gas has enormous lifting power, and if it was not for that I would not dare make such a large and comfortable airship. As it is, we can sail through the air as easily as if we were on an ocean liner on the sea and much more quickly. "I generate the gas in the engine room as I need it," the professor went on. "It goes to the oiled silk bag through two tubes. When we have arisen to a sufficient height I start the electric engine, the propeller whirls around, and the ship moves forward, just as a steamboat does when the screw is set in motion. Then all I have to do is to steer." "It's great!" cried Jack with sparkling eyes. "It certainly is," agreed Mark.