Take a square sheet of paper of convenient size, say a foot square. Divide it by lines drawn at right angles into five hundred and seventy-six squares, twenty-six each way; in the upper horizontal row write the alphabet in its natural order, one letter in each square; in the second horizontal row write the alphabet, beginning with B. There will then be one square left at the end of this row; into this put A. Fill the third row by beginning with C, and writing A and B after Z at the end. So on until the whole sheet is filled. When completed, the table, if correct, will present this appearance. In the upper horizontal row, the alphabet in its natural order from left to right; in the left-hand vertical row, the same from top to bottom; and the diagonal, from upper right to lower left-hand corner, will be a line of Z’s. Each party must have one of the tables. A key-word must be agreed upon, which may be any word in the English language, or from any other language if it can be represented by English letters, or, indeed, it may even be a combination of letters which spells nothing. Now, to send a message, first write the message in plain English. Over it write the key-word, letter over letter, repeating it as many times as it is necessary to cover the message. Take a simple case as an illustration. Suppose the key-word to be _Grant_, and the message _We have five days’ provisions_. It should be placed thus:— Grantgrantgrantgrantgran Wehavefivedaysprovisions Now find, in the upper horizontal row of the table, the first letter of the key-word, G, and in the left-hand vertical column, the first letter of the message, W. Run a line straight down from G, and one to the right from W, and in the angle where the two lines meet will be found the letter which must be written as the first letter of the cipher. With the second letter of the key-word, R, and the second letter of the message, E, find in the same way the second letter of the cipher. The correspondent who receives the cipher goes to work to translate it thus:—He first writes over it the key-word, letter over letter, repeating it as often as necessary. Then finding in the upper row of his table the first letter of the key-word, he passes his pencil directly down until he comes to the first letter or the cipher; the letter opposite to it in the left vertical column is the first letter of the translation. Each of the succeeding letters is found in a similar way.