g, with all his marvelous quickness of muscular control, to cut shorter and ever shorter the time between the opening and the closing of the switch. At last he arranged a powerful electro-magnetic device so that one impulse would both open and close the switch, with an open period of one one-thousandth of a second. Only then was he satisfied.

"A thousandth is enough to give us a look around, due to persistence of vision; and it is short enough so that they won't see it unless they have a recording observer on us. Even if they still have rays on us, they can't possibly neutralize our screens in that short an exposure. All right, gang? We'll take five visiplates and cover the sphere. If any of you get a glimpse of him, mark the exact spot and outline on the glass. All set?"

He pressed the button. The stars flashed in the black void for an instant, then were again shut out.

"Here he is, Dick!" shrieked Margaret. "Right here—he covered almost half the visiplate!"

She outlined for him, as nearly as she could, the exact position of the object she had seen, and he calculated rapidly.

"Fine business!" he exulted. "He's within half a mile of us, three-quarters on—perfect! I thought he'd be so far away that I'd have to take photographs to locate him. He hasn't a single ray on us, either. That bird's goose is cooked right now, folks, unless every man on watch has his hand right on the controls of a generator and can get into action in less than a tenth of a second! Hang on, gang, I'm going to step on the gas!"

After making sure that everyone was fastened immovably in their seats he strapped himself in the pilot's seat, then set the bar toward the strange vessel and applied fully one-third of its full power. The Skylark, of course, did not move. Then, with bewildering rapidity, he went into action; face glued to the visiplate, hands moving faster than the eye could follo