Whitney was not
back when I arrived, but the clerk was there, and I could not very
well just leave the letter on the table again.
"Mr. Kennedy would like to know when he can see Mr. Whitney," I
said, on the spur of the moment. "Can't you call him up again?"
The clerk, as I had anticipated, went into Whitney's office to
telephone. Instead of laying the letter on the table, which might
have excited suspicion, I stuck it in the letter slot of the door,
thinking that perhaps they might imagine that it had caught there
when the postman made his rounds.
A moment later the clerk returned. "Mr. Whitney is on his way down
now," he reported.
I thanked him, and said that Kennedy would call him up when he
arrived, congratulating myself on the good luck I had had in
returning the letter.
"What is it?" I asked, a few minutes later, when I had rejoined
Craig in the laboratory.
He was poring intently over what looked like a negative.
"The possibility of reading the contents of documents inclosed in
a sealed envelope," he replied, still studying the shadowgraph
closely, "has already been established by the well-known English
scientist, Dr. Hall Edwards. He has been experimenting with the
method of using X-rays recently discovered by a German scientist,
by which radiographs of very thin substances, such as a sheet of
paper, a leaf, an insect's body, may be obtained.
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