more tenuous and gradually dissipated into nothingness.
With an exclamation of satisfaction, Dr. Bird bent down and thrust the
end of a cylinder under the building. He removed it in a moment as the
fog began to stream from the upper end. Carefully he closed the
pet-cocks of the tube and replaced it in the car. He filled a half
dozen tubes before he was satisfied.

"I'd like to go down to the water," he said through his mask. "What
kind of a jigger do they run on that track?"

"It's a Ford scooter, I was told. It's probably in that shed."

* * * * *

Half an hour later the two men were running the scooter down the four
miles of narrow gage track which separated Michaelville from the Bush
River. A few scattered patches of fog could be seen on either side of
the track, but none were of sufficient thickness to warrant much
success in sample taking. At the water front Dr. Bird looked across
the half mile wide river and grunted.

"The tide won't be in for another three hours," he said. "Right now
there isn't over sixteen inches of water in there."

Carnes was waiting in the well lighted laboratory when they drove up.

"All right, Davis," said the doctor, "get busy on those samples. If
you can't make out the first two, don't crack the others but leave
them for me. Give Carnes your mask; he'll drive the rest of the night.

"What luck, Carnesy?" he asked, as the detective, wearing Davis' mask,
drove toward the officers' club.

"No stray plane landed or even flew over here last night so far as I
could learn. Most of the boats on the bay were either known or lent
themselves to ready identification. There were four that I couldn't
exactly place, but I think we can safely discard all but one. Some
fishermen were pulling nets on the bay about half a mile outside the
mouth of the Bush River last night. About eleven, a boat running
without lights passed them. They said that they could not hear an
engine running, but just a dull hum and the gurgle of a propeller.
They hailed it, but got no answer. It faded away into the darkness and
they think it was headed toward the mouth of the Bush River. They had
their nets up and reset in another hour but the boat didn't
reappear."

"Hmm. High tide was at ten minutes after midnight. There was plenty of
water in the river at that hour. It sounds promising."

"I thought of telephoning Washington and getting a Coast Guard cutter
put on patrol in the bay bu