Here in the open sunshine
by this window I am going to place these two sheets of paper side by
side. It will take longer than I care to wait to make my demonstration
complete, but I can do enough to convince you."
For a quarter of an hour we sat in silence, wondering what he would do
next. At last he beckoned us over to the window. As we approached he
said, "On sheet number one I have written with quinoline; on sheet
number two I wrote with a solution of nitrate of silver."
We bent over. The writing signed "Thurston" on sheet number one
was faint, almost imperceptible, but on paper number two, in black
letters, appeared what Kennedy had written: "Dear Harris: Since we
agreed to disagree we have at least been good friends."
"It is like the start of the substituted letter, and the other is like
the missing note," gasped Leland in a daze.
"Yes," said Kennedy quickly. "Leland, no one entered your office. No
one stole the Thurston note. No one substituted the Lytton letter.
According to your own story, you took them out of the safe and left
them in the sunlight all day. The process that had been started
earlier in ordinary light, slowly, was now quickly completed. In other
words, there was writing which would soon fade away on one side of the
paper and writing which was invisible but would soon appear on the
other.
"For instance, quinoline rapidly disappears in sunlight. Starch with a
slight trace of iodine writes a light blue, which disappears in air.
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