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16 that the point rests upon the exact latitude and longitude of Helium. Then I start the engine, roll up in my sleeping silks and furs, and with 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