crazy machinist who tried to wreck the projectile?"

"Because I once saw some of the crazy letters he sent us, and he wrote
just like the man who gave Dick this note. But come on, let's hustle,
and see what's up."

In a few minutes they came in sight of the white bridge, which was
about a quarter of a mile down the road from the professor's house. The
two boys kept well together, and they were watching for a first sight
of the man in waiting.

"See anything?" asked Jack.

"No; do you?"

"Not a thing. Wait until we get closer. He may be in the shadow. It's
dark now."

Almost as Jack spoke, the moon, which had been hidden behind a bank of
clouds, peeped out, making the scene comparatively bright. The boys
peered once more toward the bridge, and, as they did so, they saw a
figure step from the shadows, stand revealed for an instant in the
middle of the structure, and then, seemingly after a swift glance
toward the approaching chums, the person darted off in the darkness.

"Did you see that?" cried Jack.

"Sure," assented Mark. "Guess he didn't want to wait for us. Why, he's
running to beat the band!"