"Well, we won't discuss it now," went on the captain. "Are you all ready, Mr. Hamilton?"
"All ready, yes, sir."
The captain and Lieutenant Larson took their places, one on either side of Dick. Some of the orderlies at the Academy had been detailed to assist in the start, holding back on the biplane until the engine had attained the necessary speed.
There was an arrangement whereby the machine could be held in leash, as it were, by a rope, and when the necessary pressure developed from the propeller blades, the rope could be loosed from the aviator's seat. But that attachment was not in use at Kentfield then.
The powerful motor hummed and throbbed, for a muffler was temporarily dispensed with on account of its weight. Every unnecessary ounce counts on an airship, as it is needful to carry as much oil and gasolene as possible, and the weight given over to a muffler could be more advantageously applied to gasolene, on the smaller craft.
Faster and faster whirled the big blades, cutting through the air. The captain kept his eyes on a balance scale, by which was registered the pull of the propellers.
"That's enough!" he cried. "Let her go!"
Dick felt the machine move slowly forward on the rubber tired bicycle wheels over the grassy starting ground, gradually acquiring speed before it would mount upward into the air.
Perhaps a word of explanation about airships may not be out of place. Those of you who know the principle on which they work, or who have seen them, may skip this part if you wish.
The main difference between a balloon and an aeroplane, is that the balloon is lighter than air, being filled with a very light gas, which causes it to rise.