Let us begin by describing the code with which the Professor apprises Mlle. C of the various numbers chosen by the audience.
The units are expressed by letters from which Prof. B forms sentences when addressing Mlle. C. A very commonly used code is this:—
| 1 | is represented by | t | |
| 2 | „ | „ | n |
| 3 | „ | „ | m |
| 4 | „ | „ | r |
| 5 | „ | „ | l |
| 6 | „ | „ | h |
| 7 | „ | „ | k, g, or c |
| 8 | „ | „ | f, v, or w |
| 9 | „ | „ | p or b |
| 0 | „ | „ | s or z |
To use this code properly two things are necessary. Mlle. C must know how many figures the number consists of, and she must also know when the code is finished.
The latter point is easily settled. When she hears the words, “if you please,” she knows that whatever follows has no code meaning whatever, whilst everything that precedes these words carries a hidden meaning.
By the use of the following words the number of figures is conveyed in a perfectly unmistakable manner.
| For | one | figure | use the word | figure. | |
| „ | two | figures | „ | „ | number. |
| „ | three | „ | „ | „ | very well. |
| „ | four | „ | „ | „ | very well, sir (Mlle. or madam). |
| „ | five | „ | „ | „ | very good. |
| „ | six | „ | „ | „ | very good, sir (or madam). |
The following explanation shows how to put this into practice. Taking all the numbers successively from one to ten (a thing that would never be done in an ordinary way), Prof. B conveys to his fair friend the desired information by means of the sentences subjoined.
| Prof. | — | Tell this figure. (t = 1; “figure” = one number.) |
| „ | Now, what is this figure? (n = 2.) | |
| „ | Might I ask this figure? (m = 3.) | |
| „ | Repeat this figure. (r = 4.) | |
| „ | Let me know this figure. (l = 5.) | |
| „ | Have you understood? (h = 6.) | |
| „ | Give me this figure. (g = 7.) | |
| „ | Will you repeat this? (w = 8.) | |
| „ | Please tell me this figure. (p = 9.) |
Prof.—This seems an easy number. (t = 1, s = 0; “number” means two figures. Ans. 10.)