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.