* * *

Tommy went on with his work. The essential defect in the catapult
Denham had designed was the fact that it practically had to be rebuilt
after each use. And, moreover, the metallic ammonium was so fugitive a
substance that it was hard to keep. Once it had been strained by
working, it gradually adverted to a gaseous state and was lost. And
while he still tried to keep the little catapult in a condition for
use, he was at no time sure that he could send a pair of automatics
and ammunition through in a steel box at any moment that Denham came
close enough to notice a burning smoke-fuse attached.

But he was working on another form of catapult entirely, now. In this
case he was using hollow magnets placed at known angles to each other.
And they were so designed that each one tended to adjust its own
hollow bore at right angles to the preceding one, and each one would
take any moving, magnetic object and swing it through four successive
right angles into the fifth dimension.

He fitted the first magnet on twin rods of malleable copper, which
also would carry the current which energized the coil. He threaded the
second upon the same twin supports. When the current was passed
through the two of them, the magnetic field itself twisted the
magnets, bending the copper supports and placing the magnets in their
proper relative positions. A third magnet on the same pair of rods,
and a repetition of the experiment, proved the accuracy of the idea.
And since this device, like the dimensoscope, required only a
forty-five degree angle to our known dimensions, instead of a right
angle as the other catapult did, Tommy was able to work with ordinary
and durable materials. He fitted on the last two coils and turned on
the current for his final experiment. And as he watched, the twin
three-eighths-inch rods twisted and writhed in the grip of the
intangible magnetic force. They bent, and quivered, and twisted....
And suddenly there seemed to be a sort of inaudible _snap_, and one of
the magnets hurt the eyes that looked at it, and only the edge of the
last of the series was visible.

* * * * *

Tommy drew in his breath sharply. "Now we try it," he said tensely. "I
was trying to work this as the mirrors of the dimensoscope were
fitted. Let's see."

He took a long piece of soft-iron wire and fed it into the hollow of
the first magnet. He saw it come out and bend stiffly to enter the
h