perimental models, the propulsion impulse must originate
from the base."

So they descended the stairs, entered another dark corridor, found
another switch and pressed it, and thus they proceeded, lighting the
interior of the rocket as they went. And as they descended, the roar
of the exhaust increased in volume, indicating that they were nearing
its source.

Presently they entered a large, circular room with an illuminated dial
at the far end. Drawing near, they saw a confusion of instruments that
for a moment left them dazed.

While Stoddard studied them in bewilderment, Prescott circled the room
till he found a switch. Pressing it, he produced a brilliant flood of
illumination.

"Now then, let me have a look at this," he said, returning to the
dial. "Professor Goddard once explained to me the workings of one of
his experimental models. The motive force must be some liquefied
mixture, possibly oxygen and hydrogen. Some of these instruments--most
of them, in fact--must be valves."

He touched one, turned it, and the rocket responded with a sickening
burst of speed.

"No, that won't do! We're going plenty fast enough now!"

He touched another, and they slacked off dizzyingly.

"Well, there are two controls, anyway. Now then, how do they steer
this thing? That is the next problem we must solve."

But though he touched this instrument and that, producing weird
effects, their course continued in the direction set. And meanwhile,
they were hurtling outward through space at a rate of speed he knew
would presently carry them beyond the gravitational pull of the earth.

Then, as he grasped and swung down a curious lever that worked in a
quadrant, they felt a violent lunge to the left, and for a moment it
seemed they would shoot to the ceiling.

"Good God!" gasped Stoddard. "What's happened?"

"Nothing--only that I've found how to steer this wild steed!" cried
the professor, exultantly.

* * * * *

It was really quite simple, he explained, as he eased up on the lever.
In application, it was a development of the gyroscope principle, that
a wheel revolving freely within a freely suspended frame tends to make
the frame revolve in the other direction.

"You see, the rocket is the freely suspended frame," he went on,
"while this lever controls a gyroscopic wheel somewhere. To set it
spinning to the right causes us to turn to the left, and vice versa."

"But you almost stood us on o