He pointed to the other two, which, as he said, were turning over noiselessly and with a rhythm that told its tale plainly. Even Dick had sufficient experience of this class of engine to know that the running was excellent. But beyond that he was somewhat fogged. For besides some machinery housed in at the end of each motor, and a certain number of switches and levers common to any engine-room, there was nothing to indicate in what manner the power of the engines was conveyed, nor in what direction. Where was the propeller? How did these motors operate it? By electricity? Perhaps, for he could see a large dynamo revolving at the far end of the cabin. But he was by no means certain. He asked the question instantly, causing Joe to raise his head, open a port at the far end of the cabin, and invite him to look through it. "We're a little aft of amidships here," he explained, "and form the lowest attachment to the vessel. We're dead in the central line, and the weight of these motors and of other accessories housed in what compares with the keel of an ordinary ship, keeps her perfectly steady. Now, look yonder. That is the tail end of the ship. You can see the propeller, and as it is revolving and you cannot, therefore, distinguish its outline I had better tell you something about it. To begin, it's both propeller and rudder. See, I wish to turn the vessel. I press this lever to the right and at once the propeller swings in the same way, driving the tail of the ship to the left. See, I reverse the motion. Or, perhaps, I wish to descend or rise--hold tight, please, gentlemen, while I give our friend here a little demonstration! But first, let me say that the propeller itself is forty feet in diameter, presents half a dozen blades, the pitch of which can be instantly altered, while the blades are encircled by a tube some twenty feet in depth from back to front. Thus the air drawn into this revolving tube cannot escape to either side, and the blades lose no efficiency, while one can readily understand that when the ship is travelling quickly, particularly against a head wind, the alteration in the pitch of the blades makes for greater speed and more effectual use of the power. Now, hold tight, please. We'll show our friend of what we are capable."