s it matter how often a letter is repeated;
neither is one held to one word: it may be two or three or any
reasonable number. Simply apply it to the alphabetic Blocked-Out Square
and the message is evident; no books whatever are required. A slip of
paper and a pencil are all that are necessary; any one can write the
square; there is not any secret as to it. The secret is the key-word.

Harleston took a sheet of paper and wrote the square:

ABCDEFGHIJKLMNOPQRSTUVWXYZ
BCDEFGHIJKLMNOPQRSTUVWXYZA
CDEFGHIJKLMNOPQRSTUVWXYZAB
DEFGHIJKLMNOPQRSTUVWXYZABC
EFGHIJKLMNOPQRSTUVWXYZABCD
FGHIJKLMNOPQRSTUVWXYZABCDE
GHIJKLMNOPQRSTUVWXYZABCDEF
HIJKLMNOPQRSTUVWXYZABCDEFG
IJKLMNOPQRSTUVWXYZABCDEFGH
JKLMNOPQRSTUVWXYZABCDEFGHI
KLMNOPQRSTUVWXYZABCDEFGHIJ
LMNOPQRSTUVWXYZABCDEFGHIJK
MNOPQRSTUVWXYZABCDEFGHIJKL
NOPQRSTUVWXYZABCDEFGHIJKLM
OPQRSTUVWXYZABCDEFGHIJKLMN
PQRSTUVWXYZABCDEFGHIJKLMNO
QRSTUVWXYZABCDEFGHIJKLMNOP
RSTUVWXYZABCDEFGHIJKLMNOPQ
STUVWXYZABCDEFGHIJKLMNOPQR
TUVWXYZABCDEFGHIJKLMNOPQRS
UVWXYZABCDEFGHIJKLMNOPQRST
VWXYZABCDEFGHIJKLMNOPQRSTU
WXYZABCDEFGHIJKLMNOPQRSTUV
XYZABCDEFGHIJKLMNOPQRSTUVW
YZABCDEFGHIJKLMNOPQRSTUVWX
ZABCDEFGHIJKLMNOPQRSTUVWXY

Assume that the message to be transmitted is: "To-morrow sure," and that
the key-word is: "In the inn." Write the key-word and under it the
message:

INTHEINNINTH
TOMORROWSURE

Then trace _downward_ the I column of the top line of the square, and
_horizontally_ the T column at the side of the square until the two
lines coincide in the letter B: the first letter of the cipher message.
The N and the O yield B; the T and the M yield F; the H and the O yield
V, and so on, until the completed message is:

BBFVVZBJAHKL

The translator of the cipher message simply reverses this proceeding. He
knows the key-word, and he writes it above the cipher message:

INTHEINNINTH
BBFVVZBJAHKL

He traces the I column until B is reached; the _first_ letter in that
line, T, is the first letter of the message--and so on.

Simple! Yes, childishly simple with the key-word; and the key-word can
be carried in one's mind. Without the key-word, translation is
impossible.

Harleston put down the paper and leaned back.

Altogether it was a most interesting collection, these four articles on
the table. It was a pity that the cab and the sleeping horse were not
among the exhibits. Number one: a lady's lace handkerchief. Number two:
thr