"The next compartment for'ard contains the mechanism for actuating the vertical rudders. Above that are the motor-rooms, while right for'ard are the twin navigation-rooms. We'll have a look at the motor-rooms first of all. By the by, those are the cylinders for storing the ultra-hydrogen under pressure. At the present moment the dead weight of this section is less than fifty pounds."
"But we weigh more than that," observed Dacres.
"Quite so; but the buoyancy is automatically maintained. As you crossed the threshold of the doorway you stepped upon a plate resembling the floor of aweigh-bridge. At once a sufficient quantity of ultra-hydrogen is introduced into the ballonettes to counteract your weight, and, in fact, the weight of any person or article brought on board."
"I'm afraid I'm curious," said Dacres, "but what will happen when we go 'ashore'? Will the volume of the gas in the ballonettes be correspondingly reduced?"
"Yes, but not wholly automatically. You will have to record your weight on an indicator, and the adjustment then takes place. That dial you see on the bulkhead gives the total lifting power of the whole of the ballonettes. That instrument to the left makes the necessary compensating adjustments to the airship according to the temperature, altitude, and amount of moisture in the air."
In the starboard engine-room Dacres noticed that each of the two motors had four cylinders of comparatively small bore considering the horsepower developed.
"These are not air-cooled?" he asked pointing to the motors.
"No, water-cooled. This system serves a dual purpose, for the water circulates throughout all the cabins of the section, and if necessary through Nos. 2 and 3 section as well, thus affording a warmth that is appreciated when we are flying at a great altitude. Ten to twelve thousand feet is our favourite height, for then we can command a field of vision—provided the atmosphere is clear—of anything up to one hundred and twenty miles. Now for the upper navigation-room—your future post."
This compartment was situated under the commencement of the tapering portion of the envelope, its roof and walls being formed by the rounded surface of the outer skin. Here there were several observation panes, so that a fairly extensive view could be obtained. It was impossible, however, to see immediately below, and on this account the necessity of a second navigation-room was apparent.
It reminded Dacres strongly of the conning-tower of a battleship, except that the scuttles were much larger than the slits in the armoured walls of the latter. A standard compass, chart-table, gauges, indicator, voice-tubes, and telephones left very little space unoccupied.