accidentally. The gem-boxes had been packed at various times, and hence the uniformity of the hairs connected them definitely with the person who packed the boxes. In short, it seemed at first sight practically certain that they were the hairs of the actual robber; in which case we could say that the robber was a man with a short light-brown moustache.
“But when I came to reflect on the facts observed I was struck by their singularity. Moustache hairs are shed very freely, but they do not drop out at regular intervals. One, two, or more hairs in any one box would not have been surprising. A man who was in the habit of pulling at or stroking his moustache might dislodge two or three at once. The surprising thing was the regularity with which these hairs occurred; one, and usually one only, in each box, and no complete box in which there was none. It was totally opposed to the laws of probability.
“The point was highly significant. Anyone can recognize a hair. Most men can recognize a moustache hair. A detective certainly could. If these boxes had been opened by the police, as Hollis had originally intended, these hairs would almost certainly have been seen and eagerly fastened on as giving what would amount to a description of the thief. They would have been put in evidence at the trial and would have been perfectly convincing to the jury.
“The more I reflected on the matter the more did I suspect those hairs. If one assumed that they had been planted deliberately, say by a clean-shaved or dark-haired criminal, their regular occurrence in every box would be quite understandable. It would be a necessary precaution against their being overlooked. Otherwise it was unaccountable. Still, the fact of their presence had to be noted and the individual from whom they came identified, if possible.
“The second discovery that I made was, perhaps, even more odd. In every one of the boxes I found particles of the fine dust which falls out of the holes in worm-eaten wood; sometimes only a few grains, sometimes quite a large number of grains, and in the aggregate a really considerable quantity.”
“But how astonishing,” exclaimed Betty, “that you should be able to tell at once that these tiny grains came from worm-eaten wood.”
“I make it my business,” he replied, “to be able to recognize the microscopical appearances of the different forms of dust. But your remark indicates a very significant point. I imagine that there will be very few persons in the world who could identify these particles in a collection of miscellaneous dust. And therein lay the value of this discovery; for if the significance of the hairs was open to doubt, that of the wood certainly was not. There was no question of its having been purposely planted. It had certainly found its way into the boxes accidentally, and the person who had unconsciously introduced it was pretty certainly unaware of its presence. It was undoubtedly a genuine clue.
“The discovery of this characteristic dust raised several questions. In the first place, how came it into the boxes? Dust from worm-eaten furniture falls on the floor and remains there. It is too coarse and heavy to float in the air like the finer kinds of dust. In a room in which there is worm-eaten furniture, you will find the particles of dust all over the floor; but you will not find any on the tables or chair-rails or mantelpiece. But these boxes must have stood on a table or bench when they were being packed and when the dust got into them. Then the dust must have been on the table or bench. But how could it have got there? It was possible that the bench, itself, might have been worm-eaten. But that was not a probable explanation, for the dust tends to fall, not to rise. It would have fallen, for the most part, from the under surface on to the floor. The most likely explanation emerged from a consideration of the next question; which was, how could one account for the large quantity that was found?
“The quantity was extraordinarily large. From the whole set of boxes we collected something approaching a quarter of a thimbleful; which seems an enormous amount if you consider that it must all have got into the boxes during the short time that they were open for packing. What could be the explanation?
“There were two factors which had to be considered: the nature of the wood and the nature of the object which had been fashioned from it; and both were important for purposes of identification. Let us consider the first factor—material. Now, these wood-boring insects do not bore through wood as the bookworm bores through paper, to get at something else. They actually feed upon the wood. Naturally, then, they tend to select the kind of wood which contains the most nourishment and which, incidentally, is usually the softest. But of all woods those of the fruit trees are richest in gum and sap and are most subject to the attacks of the worm. Walnut, pear, apple, plum, and cherry all have this drawback, and of these cherry is so inveterately ‘wormy’ that it has usually been shunned by the cabinet-maker. Now, the quantity of the wood-dust pointed to some excessively worm-eaten object and suggested one of the fruit woods as the probable material, and the balance of probability was in favour of cherry; and this was supported by the pinkish colour of the dust. But, of course, this inference was purely hypothetical. It represented the general probabilities and nothing more.
“And now we come to the second factor. What was the nature of this wooden object? A piece of ordinary furniture we could dismiss for two reasons: first, the dust from such a piece will ordinarily fall upon the floor, from whence it could hardly have got into the boxes; and, second, no matter how badly wormed a piece of furniture may be, the quantity of dust which falls from it is relatively small and accumulates quite slowly, being practically confined to that which is pushed out of the holes by the movements of the insects within. This process would not account for the great quantity indicated by these samples of ours. My feeling was that this worm-eaten object was an appliance of some sort, subject to frequent and violent disturbance. Let us take an imaginary case as an illustration. Let us imagine a mallet with an excessively worm-eaten head. Whenever that mallet is used, the shock of the impact will send a shower of wood-dust flying out on the bench, where it will rapidly accumulate.
“But, of course, this object of ours could not be a mallet for the reason that mallets are always made of hard wood; and jewellers’ mallets are usually made of box-wood, lignum vitae or horn, none of which is subject to ‘the worm.’ Thinking over the various appliances used by jewellers—since it was with a jeweller we were dealing—I suddenly bethought me of one which seemed to fulfil the conditions exactly. Jewellers and goldsmiths, as you probably know, use a variety of miniature anvils, known as stakes, bec irons, sparrowhawks, etc. Now, these little anvils are usually stuck in a block of wood, just as a smith’s anvil is planted on a tree-stump. These blocks are not usually hard wood; indeed, soft wood is preferable as it absorbs the shock better. A favourite plan is to get a little log of wood and set the spike of the stake or sparrow-hawk in a hole bored in the end grain; and the most abundant source of these little logs—at least in the country—is the pile of trimmings from old fruit trees. Such a log would tend very soon to become worm-eaten; and if it did, every time it was used a ring of wood-dust would form around its base and would soon spread all over the bench, sticking to everything on it and straying on to the hands, arms, and clothing of the workman.
“This inference, you will observe, was, like the previous one, purely hypothetical. But it agreed perfectly with the observed facts and accounted for them in a reasonable way; and as I could think of no other that did, I adopted it with the necessary reservations. But, in fact, the correctness or incorrectness of this hypothesis was at present of no great importance. Apart from any question as to its exact origin, the wood-dust was an invaluable clue. We now knew that the unknown robber was a person whose clothing was more or less impregnated with wood-dust; that any places that he had frequented would yield traces of wood-dust from the floors, and that the place where the boxes had been packed abounded in wood-dust and contained a badly worm-eaten wooden object of some kind.
“The next proceeding was obvious. It was to find the places which had been frequented by that unknown person, to seek for the worm-eaten object, and, if possible, to identify the individual who appeared to be connected with it. The suspected places were two: Mr. Hollis’s house and Mr. Woodstock’s office. I did not, myself, suspect Hollis; but nevertheless I determined to examine his house as narrowly as the other. Accordingly I asked Mr. Penfield to obtain facilities for me to visit both places to make inquiries on the spot; which he did.
“Perhaps, before I describe that voyage of exploration, it may be as well to pause and consider what knowledge I now possessed and what