which is evidence, is got rid of in a safe and effectual way--a thing that couldn't be done as well by merely flinging it away on or near the premises, where it might be found. Next, the message is perfectly secret--the messenger could never guess what the key meant, nor could any other person not in the confederate's confidence. And, at the same time, the key tells all that is necessary; the robbery has been effected--come and remove the plunder. "But something unforeseen happens. No sooner are the bonds stolen and safely hidden than you go to the box, find something wrong with the lock, break it open and discover the loss. This was a thing that they trusted would not happen till after the bonds were safely got away. More, I am sent for, the clerks are kept in from lunch, and so on. Henning gets into a funk, and resolves to send a message of special urgency to his confederate. For that purpose he uses a cypher which the two have agreed upon--the most ingenious cypher I have ever seen used for the purpose. He doesn't wish to make his message any more conspicuous than he need, so he writes his cypher on this scrap of paper and rolls it inside the key--probably another expedient agreed upon in case of necessity. Then the key goes into an envelope, for greater security of the cypher message, and the messenger gets it when Henning is at last released for lunch. What happened to the message we know; and here it is. "Now I will not weary you with a detailed account of the different ways in which I attacked this cypher, but I will take the shortest possible cut to the true interpretation. A very short examination of the cryptogram shows that while no number is included above 23, the numbers, in their relative frequency, roughly agree with the relative frequency of the corresponding letters of the alphabet, _a_ for 1, _b_ for 2, and so on." Here I handed Hewitt the pencilled note I had made at the hospital, with letters substituted for the figures, thus:--_i, h, n, d, t, r, e, i; o, s, t, 0, c, i, h, e; c, w, 0, 0, e, m, n, s; s, t, 0, 0, 0, 0, f, a; e, t, 0, 0, 0, 0, c, v; a, o, 0, 0, 0, 0, r, e; a, h, t, k, r, i, e, t; l, e, w, n, n, a, a, t._ Hewitt took the paper and went on. "If that were all the thing would be childishly simple. But you will see that we seem as far from the solution as ever; for the letters as they stand mean nothing, though in fact they are in normal relative frequency; so that if they mean other letters, all the rules are upset, and we are at a standstill. I admit that for a long time the thing bothered me. But a peculiarity struck me. Not only were the figures, or letters, disposed in groups of _eight_, but there were also _eight_ such groups--sixty-four altogether. What did that suggest? What but a chessboard?" "A chessboard?" I queried. "Just so--a chessboard. Eight squares each way--sixty-four altogether. So I drew a rough representation of a chessboard, and set out the letters on it, in their order, like this:--