ined a dozen pieces carefully.

"It's all fogged in exactly the same way, Doctor," he said. "The only
piece of clear glass in the room is that piece of plate glass on your
desk."

* * * * *

Dr. Bird picked up a hammer and struck the plate on his desk a sharp
blow. Carnes ducked instinctively, but the hammer rebounded harmlessly
from the plate.

"That isn't glass, Carnes," said the doctor. "That plate is made of
vitrilene, a new product which I have developed. It looks like glass,
but it has entirely different properties. It is of enormous strength
and is quite insensitive to shock. It has one most peculiar property.
While ultra-violet and longer rays will penetrate it quite readily, it
is a perfect screen for X-rays and other rays of shorter wave length.
It appears to be the only piece of transparent substance in my
laboratory which has not been fogged, as you call it."

"Do short waves fog glass, Doctor?"

"Not so far as I know at present, but you must remember that very
little work has been done with the short wave-lengths. In the vast
range of waves whose lengths lie between zero and that of the X-ray,
only a few points have been investigated and definitely plotted. There
may be in that range a wave-length which will fog glass."

"Then your theory is that some sort of a ray machine was put in
operation before the helicopter landed?"

"It is too early to attempt any theorizing, Carnes. Let us confine
ourselves to the known facts. Lieutenant Breslau was normal at
midnight and was working in this room. Some time between then and
seven this morning he underwent certain mental and physical changes
which prevent him from telling us what he observed. During the same
period, a hole was cut in the roof and things of great importance
stolen. At the same time, all the glass in the laboratory became
semi-opaque. The problem is to determine what connection there is
between the three events. I will handle the scientific end here, but
there is some outside work to be done, and that will be your share."

* * * * *

"Give your orders, Doctor," said the detective briefly.

"To understand what I am driving at, I will have to tell you what has
been stolen. Naturally this is highly confidential. Some rumors have
leaked out as to my experiments with 'radite,' as I have named the
new radium-containing disintegrating explosive on which I have been
working, but no o