Scotland Yard also discovered, probably with considerable assistance from the Censorship Department, that the Germans were successfully getting out information useful to them through open business letters addressed to residents in neutral countries, particularly Norway, Sweden, Denmark, and Holland, which were decoded by adding certain geometrical figures. For example, where the sides of an added triangle or triangles intersected one another, or cut the rim of a circle, there would be found the words used in the secret messages.
Several of these ingenious codes were described in a most interesting article which was published in Pearson's Magazine, October, 1918, with illustrations which more clearly demonstrated their latent meaning. Two of the most brilliant of them were the knot alphabet and the chess problem.
In the former case a parcel sent to a supposed prisoner in a German internment camp was found to contain, amongst other things, a woollen sweater, or knitted sports vest. It was apparently so badly knitted, and the wool was seen to be so full of knots, that the censor's suspicions were aroused. Subsequent searches revealed that no such person as the addressee of the parcel in question was known to exist. His name certainly did not appear in any Army List. The aforesaid garment was most carefully unravelled. The wool was found to be whole, with a multitude of simple knots tied at irregular intervals. Alphabets were written on a board, each letter being placed at given distances apart, and very soon a most interesting message was read off.
The chess problem was deeper in its cunning and its intricacy. During 1917, a young and fascinating actress appeared in Paris. She was suspected and closely watched. In due course she captivated one of the junior secretaries of a neutral Embassy. His integrity was absolutely beyond all doubt, but naturally he also was watched and shadowed in order to learn what was passing, or might be passing, between them or otherwise.
The watchers' notes, on being compared, revealed certain facts which when carefully pieced together laid bare the whole plot. The actress professed to be deeply interested in the serious game of chess. She inspired a similar passion in the breast of the young and inexperienced attaché. One day she produced to him a rough illustration of an alleged chess problem which she had cut from a local newspaper; in all probability she herself had indirectly caused its publication. She worried her admirer unduly to help her solve what had been, or were, the opening moves in the game which had caused the pieces to be left on the board as shown in the sketch. No one in Paris could be found who could enlighten or help her; at least, so she represented.
Gentle interrogation of the attaché by his inamorata caused him to admit the existence of a chess club of some renown in the capital of the country his Embassy represented. It was a neutral country which bordered on Germany.
The actress then persuaded him to send this simple problem to the club mentioned with an urgent request to unravel the problem, if possible, and to let her know, through him, the result.
She knew, as does everyone who has had any close relationship with an Embassy, that every Embassy has its own private letter-bag, which is inviolate, and is passed over all frontiers uncensored and unopened, and is generally carried personally by some trusted messenger of the Government interested.
The actress undoubtedly relied on the almost certain chance of her admirer sending his letters, this one in particular enclosing the problem illustration, in the Embassy letter-bag. Which indeed he did. But the very astute members of the French Secret Service were wide awake to all her carefully-thought-out plans. They took measures accordingly, and the letter in question never reached its destination.
The watchers had reported that this actress had shown strong outward charitable dispositions, particularly towards the wounded soldiers from the war; that she frequently visited them in the various hospitals, sung to them, entertained them, and took them lavish presents of fruit and flowers. On one of these most praiseworthy visits she had been observed to linger unduly at the bedside of a young German aviation officer who had been shot down well behind the French lines.