"A detectaphone wouldn't be of any use here,"
he replied. "No one is going to do any talking in that room."
Again the brace and bit were at work. At last the wall had been
penetrated, and he quickly removed every trace from the other side
that would have attracted attention to a little hole in an obscure
corner of the flowered wall-paper.
Next, he drew out what looked like a long putty-blower, perhaps a
foot long and three-eighths of an inch in diameter.
"What's that?" I asked, as he rose after carefully inserting it.
"Look through it," he replied simply, still at work on some other
apparatus he had brought.
I looked. In spite of the smallness of the opening at the other
end, I was amazed to find that I could see nearly the whole room
on the other side of the wall.
"It's a detectascope," he explained, "a tube with a fish-eye lens
which I had an expert optician make for me."
"A fish-eye lens?" I repeated.
"Yes. The focus may be altered in range so that any one in the
room may be seen and recognised and any action of his may be
detected.
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