ctor had been repaired and lubricated. The comparison between the
two gave Rick his clue.

"This is a sniper nest built by the Confederates," he guessed. "Probably
to protect the mine. The upper mine tunnel opened out here, too, and
then war came and the people sealed the upper one to give protection to
the troops working the lower level. That means the upper level was dug
out first."

"It's speculation, but it sounds good," Scotty agreed. "These are gun
ports, very likely. I don't know what other purpose they could have
served."

Later they learned from Dr. Miller that the ports had also served as
ventilation for slaves using the mine to hide on their way North to
freedom, but that was after the North had the area partly in its grip.
They also found that from these same ports the Lansdale brothers had
fired the shots that killed Captain Seth Costin, for the legend was
almost entirely true.

"We open this port in front of the machine and we'll be only inches
above the pool," Rick said. "Look at the location of the pipe. So, to
produce the ghost, the Frostola man slid open the port, dropped a piece
of dry ice...."

"All properly sized to give the right amount of mist for the right
time," Scotty added.

"... and turned on the machine. With only the small port for the sound
to go through, it wouldn't be audible to anyone in the picnic grounds."

Scotty agreed. "And since the projector is so close to the mist we
wouldn't see a beam. That lens must have a mighty wide angle, by the
way. What's more, the projector must be slid closer to the opening when
in use."

"True. You know, in a way we were unlucky. If we had chanced to climb a
tree when the ghost was actually appearing, we would have seen the
projection lens through the mist as a bright spot of light, and that
would have given the show away before this. But because of the angle,
only someone in a tree could see it."

Rick shook his head in admiration. "Rear-screen projection with a
wide-angle lens. That's really using movie technique for all it's
worth."

"Rear-screen projection?" Scotty queried.

"Sure. Movies and TV use it all the time. When the hero is supposed to
be watching dinosaurs fighting it out, he's actually standing in front
of a big screen of special plastic or ground glass, with the picture
projected on it from behind. The mist acted as the screen, so we saw the
image but not the projector beam. That's rear-screen projection."

"I know how