He placed the instrument on the thumb-print in the book, and, having carefully adjusted it, drew out his note-book and looked at my wife.
"Now, Juliet," said he, "just look through the lens and tell me the letter that indicates the position of the delta—which is actually the right delta, though it is the only one visible."
Juliet peered through the magnifying glass and studied the print for a while. At length, she looked up a little doubtfully and announced:
"It seems to me that the third line cuts right through it. So it lies half in the space C and half in D. Which of the two would you call it?"
"The rule," he replied, "is that if a character is cut by a line, it is reckoned as lying in the space outside that line."
"Then this delta lies in the space D," she concluded.
"Quite right," said he. "We will mark it D; and, as the other delta is not in the print, we must mark it simply with a query. And now we proceed to the rest of the examination, the ridge-tracing and ridge-counting. We will take the tracing first. What you would have to do if both the deltas were visible would be to follow the ridge that runs from the left delta towards the right. Obviously, it must take one of three courses: it may pass below, or outside, the right delta, or below, or inside, or it may meet, or nearly meet, the corresponding ridge from the right delta. Those are the three categories: outside, inside, or meeting, by the initials, I, M, O."
"But," objected Juliet, "as the left delta is not visible, it is impossible to trace a ridge from it."
"That might be true in some cases," replied Thorndyke, "but it is not in this, for, if you look at the print, you will see that, wherever the left delta may have been, a ridge passing from it towards the right must have passed well outside the right delta."
Juliet examined the print again and agreed that it was so.
"Very well," said Thorndyke, "then we will mark it O, and proceed to the ridge-counting, which will complete the formula. You have to count the ridges between the centre of the core and the delta. Put aside the measuring glass and use my lens instead; and I will give you a point to help you to count the ridges."
He handed her his pocket lens, and produced from his bag what looked suspiciously like a dentist’s excavator, with the sharp point of which he indicated the ridges that were to be counted. Then he laid a visiting-card on the print to give a straight line from the centre to the delta, and she proceeded to count along its edge with the point of the excavator. Having gone over the ground twice, she announced the result.
"I make it twelve. But I am not quite sure, as some of the ridges fork, and might be counted as one or two. Will you count them?"
Thorndyke took the excavator from her and rapidly checked her result.
"Yes," said he, "I agree with you. I think we may safely put it down as twelve, though the bifurcations do, as you say, create a slight ambiguity. If the other delta had been visible there would, of course, have been a second circle-reading and a second ridge-count, which would obviously have been an advantage for identification. Still, what we have done gives us the main distinctive characters of this print, and we can express them by a simple formula of a few letters and numbers. Thus, the type of pattern is a whorl, with something of the character of a twinned loop. Accordingly, we put down a W with T.L. in brackets. The core, or central character—the pair of little, loops—lies entirely in the circle A. Now, there are five kinds of ‘A’ cores: the plain eye—just a tiny circle—the eye enclosing some smaller character, the left-hand spiral, the right-hand spiral, and any other ‘A’ form of an unclassifiable type. Now, in this print, the core is a left-hand, or anti-clockwise spiral, and accordingly belongs to the category A3. The delta, we agreed, lies in the space D. The ridge-tracing was outside—O—and the ridge-count twelve. We can express all these facts in a formula, thus:
"Walter Hornby. Right thumb. W (?T.L.), A3, ?, O, D, ?, 12."
"That is concise enough," I remarked. "But, after all, it gives you only a skeleton of the pattern. It would not enable you to identify a print with any approach to certainty."
"It does not aim at certainty," he replied, "but merely at such a degree of probability as would justify action or further research. But I think you hardly appreciate the degree of probability that this formula expresses. It records five different positive characters and one negative. Now, taking the five only, if we accept the very modest chance of four to one against each of these characters being present in a print which is not Walter Hornby’s, the cumulative effect of the five together yields a chance of over a thousand to one against the print being that of some person other than Walter Hornby.
"But, for our purposes, we are not obliged to stop at these five characters. We can add others; and we can locate those others either by the use of Battley’s circles or by ridge-counting with a direction-line. For instance, in this print, to the left of the core and a little downwards, the seventh ridge shows one of those little loops known as ‘lakes,’ the ninth bifurcates, and the eleventh has another, larger lake. To the right of the core the third ridge has a small lake, the fifth ridge bifurcates, the eighth has a free end, and the tenth bifurcates. There are seven additional characters which we can add to our formula, giving us twelve characters in all, the cumulative effect of which is a probability of over sixteen millions to one against the print being the thumb-print of any person other than Walter Hornby, and that is near enough to certainty for our purpose. It would undoubtedly justify an arrest; and we could leave the final proof or disproof to the experts."
He added the extra characters to the formula in his note-book, and showed us the completed entry; which certainly afforded convincing testimony to the efficiency of the method. In fact, it impressed me—and my wife, too—so profoundly that, in an access of enthusiasm, we fell upon the Thumbograph forthwith, and with the aid of Chief Inspector Battley’s ingenious instrument, proceeded to construct formulas to express the characters of the other thumb-prints in the book, while Thorndyke smoked his pipe regarded our activities with benevolent interest, seasoned by occasional advice and criticism of the results.
"It is quite an amusing game," Juliet remarked. "If only the inventors of the Thumbograph had known of it and printed directions in the book, it might have become a fashionable drawing-room pastime, and they would have made a fortune."
"Perhaps it is as well that they did not," said I. "The Thumbograph was a dangerous toy, as we discovered—or rather, as Thorndyke did."
"Yes," Thorndyke agreed, "it was a mischievous plaything. But don’t forget that it acted both ways. If it supplied the false accusation, it also supplied the conclusive answer. Walter Hornby had more reason than any of us to regret that he ever set eyes on the Thumbograph. And it may be that he has not yet come to the end of those reasons. He has evaded justice so far. But the debt is still outstanding."
X. MR. WOODBURN’S STORY
Inventors are a much-misunderstood class. The common man, in his vanity and egotism, supposes that they exist to supply him with various commodities of which he dimly perceives the need. But this is an entirely mistaken view. The inventor produces his invention because, in the existing circumstances, it has become possible. It is true that he, himself, tends to confuse the issues by persuading himself optimistically that his invention has a real and important utility. His inventive mind goes so far as to create an imaginary consumer, so that he sees life in a somewhat false perspective. The genius who devised a family Bible which could be opened out to form a billiard table, no doubt envisaged a pious type of player who had need of some means of combining the canon of scripture with a cannon off the red; while, to the inventor of a super magic-lantern which could throw pictures on the clouds, the night sky was no more than a suitable background on which to declare the glory of Blunt’s Milky Toffee.
But this is mere self-delusion. In reality, the inventor is concerned with his invention. Its use is but a side issue which hovers vaguely on the periphery of his mental field of vision. I emphasise th
e fact, because it has a bearing on the events which I am recording. For our invaluable laboratory assistant, Polton, was an inveterate inventor, and, being also an accomplished and versatile craftsman, was able to turn out his inventions in a completely realised form.
So it happened that a certain large cupboard in the laboratory was a veritable museum of the products of his inventive genius and manual skill; examples of ingenuity—sometimes fantastically misguided—the utility of which he would expound to Thorndyke and me with pathetic earnestness and appeals to "give them a trial." There were spectacles which enabled. the wearer to see behind him, there was a periscope walking-stick with which you could see round a corner, a large pedometer with movable dials for metres and yards and a micrometer adjustment of impracticable accuracy, and all sorts of clockwork devices and appliances for out-of-the-way photographic operations. But optical instruments were his special passion, whence it followed that most of his inventions took an optical turn.
I am afraid that I did not treat these children of Polton’s imagination with the respect that they deserved. Thorndyke, on the other hand, made a point of always examining even the wildest flights of the inventor’s fancy with appreciative attention, realizing—and pointing out to me—that their apparent oddity was really due to the absence of appropriate circumstances, and that those circumstances might arise at any moment and give an unexpected value to what seemed to be a mere toy. And that was what happened on the present occasion. One of Polton’s most eccentric productions suddenly revealed itself as an invaluable instrument of research. But perhaps I am beginning the story at the wrong end. I had better turn back and take the incidents in their proper order.
It was rather late one afternoon when there arrived at our chambers a dapper, well-dressed gentleman of distinctly horsey appearance, who gave the name of Woodburn, and who, rather to my surprise, turned out to be a solicitor. He presented Mr. Brobribb’s card, on which were scribbled a few words of introduction.
"I have come to see you," he explained, "on the advice of my friend Brodribb. I came up to Town expressly to confer with him on a rather queer case that has turned up in my practice. We talked over the legal issues without coming to any very definite conclusion, but Brodribb thought that there were certain points in the case that were more in your line than in either his or mine. And I am certainly inclined to agree with him to the extent that I am decidedly out of my depth."
"And what about Mr. Brodribb?" Thorndyke asked. "He is a pretty acute lawyer."
"He is," Mr. Woodburn agreed, heartily. "But this is not altogether a question of law. There are some other points on which he thought you would be able to help us. I had better give you an outline of the case. But, first, I had better explain that I am a country practitioner with my principal office at Packington in Kent, and that my clients are chiefly the farmers and country gentlemen of the surrounding district.
"Now, one of these clients is a gentleman named Mr. Didbury Toke. He is a sort of superior dealer in works of art and antiquities. He has an office in Town, but he resides at an ancient house called Hartsden Manor in the village of Hartsden and usually spends a good deal of his time there. But from time to time he has been in the habit of taking more or less prolonged trips to the Continent for the purpose of rooting about for antiques and works of art. On these occasions it has been his custom to shut up that part of the house in which his collection is lodged, and seal all the doors and windows in any way giving access to it.
"Well, about two months ago, he set forth on one of these expeditions, and, according to his usual custom, he locked up and sealed all the approaches to the rooms containing the collection and gave the keys into my custody."
"What happened to the seal?" asked Thorndyke.
"That I can’t tell you," replied Mr. Woodburn. "He didn’t give it to me, but I have an impression that he deposited it at his bank in London. I know that he did on a previous occasion. Still, he may have carried it on his person. I happen to know that it is a large, clumsy, antique ring, which he was certainly not in the habit of wearing.
"Well, as I said, he handed the keys to me, but, at the same time, he gave me very definite instructions—in writing—that the rooms were not on any account to be entered or the seals tampered with in any way. You see that his instructions were quite explicit, and, in fact, decidedly emphatic."
"Apparently," said Thorndyke, "he allowed you no discretion and provided for no contingencies. Is that not so?"
"That is so," replied Mr. Woodburn. "His instructions amounted to an absolute prohibition of any interference with the seals or any attempt to enter the enclosed rooms. That is the matter which I have been discussing with Mr. Brodribb, and which I want to discuss with you. Because this prohibition has become highly inconvenient. Circumstances have arisen which seem to make it very desirable to enter those enclosed rooms. But before I go into those circumstances, I had better tell you a little more about the arrangements of the house and those particular rooms.
"The main part of the closed premises consists of a very large room—about forty feet long—called the great gallery; but adjoining this are three or four smaller rooms, some of which are used to house part of the collection, and some are kept as workrooms, in which Mr. Toke does his mending and other odd jobs connected with the collection. The great gallery and the rooms attached to it occupy the whole of a wing which runs at right angles to the rest of the house; and, as there is only one door giving access to the gallery and its annexed rooms, the whole group of apartments is completely cut off and isolated.
"Now the circumstances to which I referred are these. Mr. Toke’s household ordinarily consists of his housekeeper and her niece, who acts as housemaid; but, when he is away from home, a nephew of the housekeeper usually comes to stay there, so that there may be a man on the premises. He is there now; so there are three persons living in the house; and those three persons are agreed that, from time to time, they have heard sounds at night apparently coming from the great gallery. It sounds incredible, and I must admit that when they first reported the matter to me, I was disposed to be sceptical. I am not entirely unsceptical now. But they are extremely positive, and, as I said, they are all agreed. So I thought it my duty to go over to the manor house and make an inspection; and the result of that inspection was only to make the whole affair still more incomprehensible. For the seals were all intact, and there was not a sign anywhere of anyone having broken into the place."
"You examined the windows, of course?" said Thorndyke.
"Yes. There are five large windows, and I examined them all from outside by means of a ladder. They certainly had not been opened, for I could see that the catches were all in their places. But I may say that the windows are all secured from inside with screws, and those screws are sealed. Mr. Toke leaves nothing to chance."
"Could you see into the room?" asked Thorndyke.
"No. The shutters were not closed, but the windows are covered by lace or net curtains, so that, although the gallery is quite light, it is impossible to see in from the outside."
"You have spoken of the collection," said Thorndyke. "Perhaps you had better tell us something about its nature and value."
"As to its value," said Mr. Woodburn, "I believe that is very considerable, but as it consists chiefly of pottery and porcelain, Bow and Chelsea figures, bronzes, and small statuary, it would be of no interest, to a burglar—at least, that is what I understood from Mr. Toke."
"I am not sure that I agree with Mr. Toke," said Thorndyke. "Of course, since you cannot melt down porcelain figures into unrecognizable ingots, they are not suitable for the common type of burglar. The ordinary ‘fence’ would not trade in them, and they could not be offered in the open market. But they are really valuable things and fairly portable, and they would not be so very difficult to dispose of. The ordinary collector is not always as scrupulous as he might be, but there is one kind of collector who is not scrupulous at all. One may take it that a millionaire who has m
ade his millions by questionable transactions, may be prepared to spend them in a like manner. The point is of some importance; for, whereas the repeated occurrence of these sounds—assuming them to have occurred—is not consistent with the idea of an ordinary burglary, it does suggest the bare possibility of some enterprising persons quietly removing the more valuable parts of the collection piecemeal."
"You do, then, really entertain the possibility that these sounds are not merely imaginary?"
"I have an entirely open mind," replied Thorndyke. "But I understood you to say that you had gone into the question of fact on the spot, and that you were satisfied that the reports were sufficiently convincing to justify serious enquiry."
"That is so," said Mr. Woodburn. "But I may say that Brodribb scouted the idea. He was incredulous as to the sounds having been heard at all, seeing that the closed rooms are so completely isolated and so distant from the rest of the house; and he suggested that if there had been any sounds, they were probably due to rats. I don’t agree with him as to the rats. Of course, I enquired whether that could be the explanation, but I think it can be excluded. The noises that rats make are pretty characteristic, and they don’t at all agree with the description of the sounds that these people gave. And they tell me that there are no rats in the house, which seems to settle the question; for, although rats will harbour in empty rooms, they don’t stay there. They must come out for food. But Brodribb’s other objection is more weighty. The great gallery is a good distance from the rest of the house. What do you really think of the probabilities?"
"Well," replied Thorndyke, "the answer to your question involves the statement of a rather bald truism. If there is no access to the closed rooms other than the door of which you spoke, and that door is still locked and the seal is still unbroken, evidently no one can possibly have entered those rooms. On the other hand, if sounds have been heard of such a nature as to make it certain that someone had entered those rooms, then it follows that there must be some means of access to those rooms other than those which are known to you. I apologize for the obviousness of the statement."
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