noise. Why wasn't that
noise heard?"

"It was heard. The watchman heard it, but knew that Lieutenant Breslau
was working here and he thought that he made the noise."

"Surely, but why didn't Breslau hear it?"

"How do we know that he didn't? He was taken to Walter Reed Hospital
this morning with his mind an absolute blank and with his tongue
paralyzed. He must have seen the thieves and they treated him in some
way to ensure his silence. When he is able to talk, if he ever is,
he'll probably give us a good description of them."

* * * * *

Dr. Bird shook his head.

"Too thin, Carney, old dear," he said. "Breslau is a very intelligent
young man. He was perfectly normal when I left him shortly after
midnight last night. He was working alone in here on a device of the
utmost military importance. On the desk is a push button which sets
ringing a dozen gongs in the building. Surely a man of that type would
have had sense enough when he heard and saw intruders cutting a hole
through the roof to sound an alarm which would have brought every
watchman on the grounds to his assistance. He must have been knocked
out before the hole was started, probably before the helicopter's
landing."

"How? Gas of some sort?"

"The windows were all closed and locked and I have already ascertained
that the gas and water lines have not been tampered with. Gas won't
penetrate through a solid roof in sufficient concentration to knock
out a man like that. It was something more subtle than gas."

"What was it?"

"I don't know yet. The clue to what it was lies, as I told you, in
those windows."

Carnes moved over and surveyed the windows closely.

"I see nothing unusual about them except that they need washing rather
badly."

"They were washed last Friday, but they do look rather dirty, don't
they? Suppose you take a rag and some scouring soap and clean up a
pane."

The detective took the proffered articles and started his task. He wet
a pane of glass, rubbed up a thick lather of scouring soap and applied
it and rubbed vigorously. With clear water he washed the glass and
then gave an exclamation of astonishment and examined it more closely.

"That isn't dirt, Doctor," he cried. "The glass seems to be fogged."

Dr. Bird chuckled.

"So it seems," he admitted. "Now look at the rest of the glass around
the laboratory."

Carnes looked around and then walked to a table littered with
apparatus and exam