an old note-book, in which were tabulated the order of letter
recurrences according to their frequency in ordinary English words, he
freshened his memory. This was the natural sequence, in direct ratio to
the use of the letters: "E: T: A: O: N: I: S: B: M, etc." The use of "E"
was double that of any other. Yet on the pages of the book he found that
the most frequently recurring symbol was "R" which was, ordinarily, one
of the least used in the alphabet. "T," which would have been second
in popularity, naturally, was seen only a few times in proportion. "Y,"
also seldom used, appeared very often. The symbol "A" was used with
surprising frequency.

"Let me see," he mused. "This code is strictly typewritten. It must be
arranged on some mechanical twist of the typing method. A is used so
many times that it might be safe to assume that it is used for a space,
as all the words in this code run together. If A is used that way,
what takes its place? S would by rights be seventh on the list, but the
average I have made shows that it is about third or fourth."

Carefully he jotted down in separate columns on a piece of paper the
individual repetitions of letters on the page of "January 7, 1915." He
arrived at the conclusion, then, that "R" was used for "E," that "S"
took the place of "A" and that "Y" alternated in this cipher for "T"
which was second on his little list.

Fur the benefit of the reader who may be interested enough to work
out this little problem, along the lines of Shirley's deductions the
arrangement of the so-called "Standard" keyboard is here shown, as it
was on the "Number Four" machine of Warren's Remwood, and the duplicate
machine which Shirley was using.

Q W E R T Y U I O P

A S D F G H J K L;

Z X C V B N M,.

Shift SPACE BAR Shift
Key Key

This diagram represents the "lower case" or small letters, capitals
being made by holding down one of the shift keys on either side, and
striking the other letter at the same time, there being two symbols on
each metal type key. As only small letters were used through the code
Shirley did not bother about the capitals. He realized at last, that if
his theory of substitution were correct the writer had struck the key
to the right of the three frequent letters. He had the inception of the
scheme.

Starting with the first line of the se