lights burning, race through the air toward Helium, confident that
at the appointed hour I shall drop gently toward the landing-stage
upon my own palace, whether I am still asleep or no."

"Provided," suggested Thuvan Dihn, "you do not chance to collide
with some other night wanderer in the meanwhile."

Carthoris smiled. "No danger of that," he replied. "See here,"
and he indicated a device at the right of the destination compass.
"This is my `obstruction evader,' as I call it. This visible device
is the switch which throws the mechanism on or off. The instrument
itself is below deck, geared both to the steering apparatus and
the control levers.

"It is quite simple, being nothing more than a radium generator
diffusing radio-activity in all directions to a distance of a
hundred yards or so from the flier. Should this enveloping force
be interrupted in any direction a delicate instrument immediately
apprehends the irregularity, at the same time imparting an impulse
to a magnetic device which in turn actuates the steering mechanism,
diverting the bow of the flier away from the obstacle until the craft's
radio-activity sphere is no longer in contact with the obstruction,
then she falls once more into her normal course. Should the
disturbance approach from the rear, as in case of a faster-moving
craft overhauling me, the mechanism actuates the speed control as
well as the steering gear, and the flier shoots ahead and either
up or down, as the oncoming vessel is upon a lower or higher plane
than herself.

"In aggravated cases, that is when the obstructions are many, or