one of the conditions of medical practice is the capability of transferring one's attention at a moment's notice from one set of circumstances to another equally important but entirely unrelated. at each visit on his round, the practitioner finds himself concerned with a particular, self-contained group of phenomena which he must consider at the moment with the utmost concentration, but which he must instantly dismiss from his mind as he moves on to the next case. it is a difficult habit to acquire; for an important, distressing or obscure case is apt to take possession of the consciousness and hinder the exercise of attention that succeeding cases demand; but experience shows the faculty to be indispensable, and the practitioner learns in time to forget everything but the patient with whose condition he is occupied at the moment.

my first morning's work on the blackmore case showed me that the same faculty is demanded in legal practice; and it also showed me that i had yet to acquire it. for, as i looked over the depositions and the copy of the will, memories of the mysterious house in kennington lane continually intruded into my reflections, and the figure of mrs. schallibaum, white-faced, terrified, expectant, haunted me continually.

in truth, my interest in the blackmore case was little more than academic, whereas in the kennington case i was one of the parties and was personally concerned. to me, john blackmore was but a name, jeffrey but a shadowy figure to which i could assign no definite personality, and stephen himself but a casual stranger. mr. graves, on the other hand, was a real person. i had seen him amidst the tragic circumstances that had probably heralded his death, and had brought away with me, not only a lively recollection of him, but a feeling of profound pity and concern as to his fate. the villain weiss, too, and the terrible woman who aided, abetted and, perhaps, even directed him, lived in my memory as vivid and dreadful realities. although i had uttered no hint to thorndyke, i lamented inwardly that i had not been given some work—if there was any to do—connected with this case, in which i was so deeply interested, rather than with the dry, purely legal and utterly bewildering case of jeffrey blackmore's will.

nevertheless, i stuck loyally to my task. i read through the depositions and the will—without getting a single glimmer of fresh light on the case—and i made a careful digest of all the facts. i compared my digest with thorndyke's notes—of which i also made a copy—and found that, brief as they were, they contained several matters that i had overlooked. i also drew up a brief account of our visit to new inn, with a list of the objects that we had observed or collected. and then i addressed myself to the second part of my task, the statement of my conclusions from the facts set forth.

it was only when i came to make the attempt that i realized how completely i was at sea. in spite of thorndyke's recommendation to study marchmont's statement as it was summarized in those notes which i had copied, and of his hint that i should find in that statement something highly significant, i was borne irresistibly to one conclusion, and one only—and the wrong one at that, as i suspected: that jeffrey blackmore's will was a perfectly regular, sound and valid document.

i tried to attack the validity of the will from various directions, and failed every time. as to its genuineness, that was obviously not in question. there seemed to me only two conceivable respects in which any objection could be raised, viz. the competency of jeffrey to execute a will and the possibility of undue influence having been brought to bear on him.

with reference to the first, there was the undoubted fact that jeffrey was addicted to the opium habit, and this might, under some circumstances, interfere with a testator's competency to make a will. but had any such circumstances existed in this case? had the drug habit produced such mental changes in the deceased as would destroy or weaken his judgment? there was not a particle of evidence in favour of any such belief. up to the very end he had managed his own affairs, and, if his habits of life had undergone a change, they were still the habits of a perfectly sane and responsible man.

the question of undue influence was more difficult. if it applied to any person in particular, that person could be none other than john blackmore. now it was an undoubted fact that, of all jeffrey's acquaintance, his brother john was the only one who knew that he was in residence at new inn. moreover john had visited him there more than once. it was therefore possible that influence might have been brought to bear on the deceased. but there was no evidence that it had. the fact that the deceased man's only brother should be the one person who knew where he was living was not a remarkable one, and it had been satisfactorily explained by the necessity of jeffrey's finding a reference on applying for the chambers. and against the theory of undue influence was the fact that the testator had voluntarily brought his will to the lodge and executed it in the presence of entirely disinterested witnesses.

in the end i had to give up the problem in despair, and, abandoning the documents, turned my attention to the facts elicited by our visit to new inn.

what had we learned from our exploration? it was clear that thorndyke had picked up some facts that had appeared to him important. but important in what respect? the only possible issue that could be raised was the validity or otherwise of jeffrey blackmore's will; and since the validity of that will was supported by positive evidence of the most incontestable kind, it seemed that nothing that we had observed could have any real bearing on the case at all.

but this, of course, could not be. thorndyke was no dreamer nor was he addicted to wild speculation. if the facts observed by us seemed to him to be relevant to the case, i was prepared to assume that they were relevant, although i could not see their connection with it. and, on this assumption, i proceeded to examine them afresh.

now, whatever thorndyke might have observed on his own account, i had brought away from the dead man's chambers only a single fact; and a very extraordinary fact it was. the cuneiform inscription was upside down. that was the sum of the evidence that i had collected; and the question was, what did it prove? to thorndyke it conveyed some deep significance. what could that significance be?

the inverted position was not a mere temporary accident, as it might have been if the frame had been stood on a shelf or support. it was hung on the wall, and the plates screwed on the frame showed that its position was permanent and that it had never hung in any other. that it could have been hung up by jeffrey himself was clearly inconceivable. but allowing that it had been fixed in its present position by some workman when the new tenant moved in, the fact remained that there it had hung, presumably for months, and that jeffrey blackmore, with his expert knowledge of the cuneiform character, had never noticed that it was upside down; or, if he had noticed it, that he had never taken the trouble to have it altered.

what could this mean? if he had noticed the error but had not troubled to correct it, that would point to a very singular state of mind, an inertness and indifference remarkable even in an opium-smoker. but assuming such a state of mind, i could not see that it had any bearing on the will, excepting that it was rather inconsistent with the tendency to make fussy and needless alterations which the testator had actually shown. on the other hand, if he had not noticed the inverted position of the photograph he must have been nearly blind or quite idiotic; for the photograph was over two feet long and the characters large enough to be read easily by a person of ordinary eyesight at a distance of forty or fifty feet. now he obviously was not in a state of dementia, whereas his eyesight was admittedly bad; and it seemed to me that the only conclusion deducible from the photograph was that it furnished a measure of the badness of the deceased man's vision—that it proved him to have been verging on total blindness.

but there was nothing startling new in this. he had, himself, declared that he was fast losing his sight. and again, what was the bearing of his partial blindness on the will? a totally blind man cannot draw up his will at all. but if he has eyesight sufficient to enable him to write out and sign a will, mere defective vision will not lead him to muddle the provisions. yet something of this kind seemed to be in thorndyke's mind, for now i recalled the question that he had put to the porter: "when you read the will over in mr. blackmore's presence, did you read it aloud?" that question could have but one significance. it implied a doubt as to whether the testator was fully aware of the exact nature of the document that he was signing. yet, if he was able to write and sign it, surely he was able also to read it through, to say nothing of the fact that, unless he was demented, he must have remembered what he had written.

thus, once more, my reasoning only led me into a blind alley at the end of which was the will, regular and valid and fulfilling all the requirements that the law imposed. once again i had to confess myself beaten and in full agreement with mr. marchmont that "there was no case"; that "there was nothing in dispute." nevertheless, i carefully fixed in the pocket file that thorndyke had given me the copy that i had made of his notes, together with the notes on our visit to new inn, and the few and unsatisfactory conclusions at which i had arrived; and this brought me to the end of my first morning in my new capacity.

"and how," thorndyke asked as we sat at lunch, "has my learned friend progressed? does he propose that we advise mr. marchmont to enter a caveat?"

"i've read all the documents and boiled all the evidence down to a stiff jelly; and i am in a worse fog than ever."

"there seems to be a slight mixture of metaphors in my learned friend's remarks. but never mind the fog, jervis. there is a certain virtue in fog. it serves, like a picture frame, to surround the essential with a neutral zone that separates it from the irrelevant."

"that is a very profound observation, thorndyke," i remarked ironically.

"i was just thinking so myself," he rejoined.

"and if you could contrive to explain what it means—"

"oh, but that is unreasonable. when one throws off a subtly philosophic obiter dictum one looks to the discerning critic to supply the meaning. by the way, i am going to introduce you to the gentle art of photography this afternoon. i am getting the loan of all the cheques that were drawn by jeffrey blackmore during his residence at new inn—there are only twenty-three of them, all told—and i am going to photograph them."

"i shouldn't have thought the bank people would have let them go out of their possession."

"they are not going to. one of the partners, a mr. britton, is bringing them here himself and will be present while the photographs are being taken; so they will not go out of his custody. but, all the same, it is a great concession, and i should not have obtained it but for the fact that i have done a good deal of work for the bank and that mr. britton is more or less a personal friend."

"by the way, how comes it that the cheques are at the bank? why were they not returned to jeffrey with the pass-book in the usual way?"

"i understand from britton," replied thorndyke, "that all jeffrey's cheques were retained by the bank at his request. when he was travelling he used to leave his investment securities and other valuable documents in his bankers' custody, and, as he has never applied to have them returned, the bankers still have them and are retaining them until the will is proved, when they will, of course, hand over everything to the executors."

"what is the object of photographing these cheques?" i asked.

"there are several objects. first, since a good photograph is practically as good as the original, when we have the photographs we practically have the cheques for reference. then, since a photograph can be duplicated indefinitely, it is possible to perform experiments on it which involve its destruction; which would, of course, be impossible in the case of original cheques."

"but the ultimate object, i mean. what are you going to prove?"

"you are incorrigible, jervis," he exclaimed. "how should i know what i am going to prove? this is an investigation. if i knew the result beforehand, i shouldn't want to perform the experiment."

he looked at his watch, and, as we rose from the table, he said:

"if we have finished, we had better go up to the laboratory and see that the apparatus is ready. mr. britton is a busy man, and, as he is doing us a great service, we mustn't keep him waiting when he comes."

we ascended to the laboratory, where polton was already busy inspecting the massively built copying camera which—with the long, steel guides on which the easel or copy-holder travelled—took up the whole length of the room on the side opposite to that occupied by the chemical bench. as i was to be inducted into the photographic art, i looked at it with more attention than i had ever done before.

"we've made some improvements since you were here last, sir," said polton, who was delicately lubricating the steel guides. "we've fitted these steel runners instead of the blackleaded wooden ones that we used to have. and we've made two scales instead of one. hallo! that's the downstairs bell. shall i go sir?"

"perhaps you'd better," said thorndyke. "it may not be mr. britton, and i don't want to be caught and delayed just now."

however, it was mr. britton; a breezy alert-looking middle-aged man, who came in escorted by polton and shook our hands cordially, having been previously warned of my presence. he carried a small but solid hand-bag, to which he clung tenaciously up to the very moment when its contents were required for use.

"so that is the camera," said he, running an inquisitive eye over the instrument. "very fine one, too; i am a bit of a photographer myself. what is that graduation on the side-bar?"

"those are the scales," replied thorndyke, "that shows the degree of magnification or reduction. the pointer is fixed to the easel and travels with it, of course, showing the exact size of the photograph. when the pointer is opposite 0 the photograph will be identical in size with the object photographed; when it points to, say, × 6, the photograph will be six times as long as the object, or magnified thirty-six times superficially, whereas if the pointer is at ÷ 6, the photograph will be a sixth of the length of the object, or one thirty-sixth superficial."

"why are there two scales?" mr. britton asked.

"there is a separate scale for each of the two lenses that we principally use. for great magnification or reduction a lens of comparatively short focus must be used, but, as a long-focus lens gives a more perfect image, we use one of very long focus—thirty-six inches—for copying the same size or for slight magnification or reduction."

"are you going to magnify these cheques?" mr. britton asked.

"not in the first place," replied thorndyke. "for convenience and speed i am going to photograph them half-size, so that six cheques will go on one whole plate. afterwards we can enlarge from the negatives as much as we like. but we should probably enlarge only the signatures in any case."

the precious bag was now opened and the twenty-three cheques brought out and laid on the bench in a consecutive series in the order of their dates. they were then fixed by tapes—to avoid making pin-holes in them—in batches of six to small drawing boards, each batch being so arranged that the signatures were towards the middle. the first board was clamped to the easel, the latter was slid along its guides until the pointer stood at ÷ 2 on the long-focus scale and thorndyke proceeded to focus the camera with the aid of a little microscope that polton had made for the purpose. when mr. britton and i had inspected the exquisitely sharp image on the focusing-screen through the microscope, polton introduced the plate and made the first exposure, carrying the dark-slide off to develop the plate while the next batch of cheques was being fixed in position.

in his photographic technique, as in everything else, polton followed as closely as he could the methods of his principal and instructor; methods characterized by that unhurried precision that leads to perfect accomplishment. when the first negative was brought forth, dripping, from the dark-room, it was without spot or stain, scratch or pin-hole; uniform in colour and of exactly the required density. the six cheques shown on it—ridiculously small in appearance, though only reduced to half-length—looked as clear and sharp as fine etchings; though, to be sure, my opportunity for examining them was rather limited, for polton was uncommonly careful to keep the wet plate out of reach and so safe from injury.

"well," said mr. britton, when, at the end of the séance, he returned his treasures to the bag, "you have now got twenty-three of our cheques, to all intents and purposes. i hope you are not going to make any unlawful use of them—must tell our cashiers to keep a bright look-out; and"—here he lowered his voice impressively and addressed himself to me and polton—"you understand that this is a private matter between dr. thorndyke and me. of course, as mr. blackmore is dead, there is no reason why his cheques should not be photographed for legal purposes; but we don't want it talked about; nor, i think, does dr. thorndyke."

"certainly not," thorndyke agreed emphatically; "but you need not be uneasy, mr. britton. we are very uncommunicative people in this establishment."

as my colleague and i escorted our visitor down the stairs, he returned to the subject of the cheques.

"i don't understand what you want them for," he remarked. "there is no question turning on signatures in the case of blackmore deceased, is there?"

"i should say not," thorndyke replied rather evasively.

"i should say very decidedly not," said mr. britton, "if i understood marchmont aright. and, even if there were, let me tell you, these signatures that you have got wouldn't help you. i have looked them over very closely—and i have seen a few signatures in my time, you know. marchmont asked me to glance over them as a matter of form, but i don't believe in matters of form; i examined them very carefully. there is an appreciable amount of variation; a very appreciable amount. but under the variation one can trace the personal character (which is what matters); the subtle, indescribable quality that makes it recognizable to the expert eye as jeffrey blackmore's writing. you understand me. there is such a quality, which remains when the coarser characteristics vary; just as a man may grow old, or fat, or bald, or may take to drink, and become quite changed; and yet, through it all, he preserves a certain something which makes him recognizable as a member of a particular family. well, i find that quality in all those signatures, and so will you, if you have had enough experience of handwriting. i thought it best to mention it in case you might be giving yourself unnecessary trouble."

"it is very good of you," said thorndyke, "and i need not say that the information is of great value, coming from such a highly expert source. as a matter of fact, your hint will be of great value to me."

he shook hands with mr. britton, and, as the latter disappeared down the stairs, he turned into the sitting-room and remarked:

"there is a very weighty and significant observation, jervis. i advise you to consider it attentively in all its bearings."

"you mean the fact that these signatures are undoubtedly genuine?"

"i meant, rather, the very interesting general truth that is contained in britton's statement; that physiognomy is not a mere matter of facial character. a man carries his personal trademark, not in his face only, but in his nervous system and muscles—giving rise to characteristic movements and gait; in his larynx—producing an individual voice; and even in his mouth, as shown by individual peculiarities of speech and accent. and the individual nervous system, by means of these characteristic movements, transfers its peculiarities to inanimate objects that are the products of such movements; as we see in pictures, in carving, in musical execution and in handwriting. no one has ever painted quite like reynolds or romney; no one has ever played exactly like liszt or paganini; the pictures or the sounds produced by them, were, so to speak, an extension of the physiognomy of the artist. and so with handwriting. a particular specimen is the product of a particular set of motor centres in an individual brain."

"these are very interesting considerations, thorndyke," i remarked; "but i don't quite see their present application. do you mean them to bear in any special way on the blackmore case?"

"i think they do bear on it very directly. i thought so while mr. britton was making his very illuminating remarks."

"i don't see how. in fact i cannot see why you are going into the question of the signatures at all. the signature on the will is admittedly genuine, and that seems to me to dispose of the whole affair."

"my dear jervis," said he, "you and marchmont are allowing yourselves to be obsessed by a particular fact—a very striking and weighty fact, i will admit, but still, only an isolated fact. jeffrey blackmore executed his will in a regular manner, complying with all the necessary formalities and conditions. in the face of that single circumstance you and marchmont would 'chuck up the sponge,' as the old pugilists expressed it. now that is a great mistake. you should never allow yourself to be bullied and browbeaten by a single fact."

"but, my dear thorndyke!" i protested, "this fact seems to be final. it covers all possibilities—-unless you can suggest any other that would cancel it."

"i could suggest a dozen," he replied. "let us take an instance. supposing jeffrey executed this will for a wager; that he immediately revoked it and made a fresh will, that he placed the latter in the custody of some person and that that person has suppressed it."

"surely you do not make this suggestion seriously!" i exclaimed.

"certainly i do not," he replied with a smile. "i merely give it as an instance to show that your final and absolute fact is really only conditional on there being no other fact that cancels it."

"do you think he might have made a third will?"

"it is obviously possible. a man who makes two wills may make three or more; but i may say that i see no present reason for assuming the existence of another will. what i want to impress on you is the necessity of considering all the facts instead of bumping heavily against the most conspicuous one and forgetting all the rest. by the way, here is a little problem for you. what was the object of which these are the parts?"

he pushed across the table a little cardboard box, having first removed the lid. in it were a number of very small pieces of broken glass, some of which had been cemented together by their edges.

"these, i suppose," said i, looking with considerable curiosity at the little collection, "are the pieces of glass that we picked up in poor blackmore's bedroom?"

"yes. you see that polton has been endeavouring to reconstitute the object, whatever it was; but he has not been very successful, for the fragments were too small and irregular and the collection too incomplete. however, here is a specimen, built up of six small pieces, which exhibits the general character of the object fairly well."

he picked out the little irregularly shaped object and handed it to me; and i could not but admire the neatness with which polton had joined the tiny fragments together.

i took the little "restoration," and, holding it up before my eyes, moved it to and fro as i looked through it at the window.

"it was not a lens," i pronounced eventually.

"no," thorndyke agreed, "it was not a lens."

"and so cannot have been a spectacle-glass. but the surface was curved—one side convex and the other concave—and the little piece that remains of the original edge seems to have been ground to fit a bezel or frame. i should say that these are portions of a watch-glass."

"that is polton's opinion," said thorndyke, "and i think you are both wrong."

"what do you say to the glass of a miniature or locket?"

"that is rather more probable, but it is not my view."

"what do you think it is?" i asked. but thorndyke was not to be drawn.

"i am submitting the problem for solution by my learned friend," he replied with an exasperating smile, and then added: "i don't say that you and polton are wrong; only that i don't agree with you. perhaps you had better make a note of the properties of this object, and consider it at your leisure when you are ruminating on the other data referring to the blackmore case."

"my ruminations," i said, "always lead me back to the same point."

"but you mustn't let them," he replied. "shuffle your data about. invent hypotheses. never mind if they seem rather wild. don't put them aside on that account. take the first hypothesis that you can invent and test it thoroughly with your facts. you will probably have to reject it, but you will be certain to have learned something new. then try again with a fresh one. you remember what i told you of my methods when i began this branch of practice and had plenty of time on my hands?"

"i am not sure that i do."

"well, i used to occupy my leisure in constructing imaginary cases, mostly criminal, for the purpose of study and for the acquirement of experience. for instance, i would devise an ingenious fraud and would plan it in detail, taking every precaution that i could think of against failure or detection, considering, and elaborately providing for, every imaginable contingency. for the time being, my entire attention was concentrated on it, making it as perfect and secure and undetectable as i could with the knowledge and ingenuity at my command. i behaved exactly as if i were proposing actually to carry it out, and my life or liberty depended on its success—excepting that i made full notes of every detail of the scheme. then when my plans were as complete as i could make them, and i could think of no way in which to improve them, i changed sides and considered the case from the standpoint of detection. i analysed the case, i picked out its inherent and unavoidable weaknesses, and, especially, i noted the respects in which a fraudulent proceeding of a particular kind differed from the bona fide proceeding that it simulated. the exercise was invaluable to me. i acquired as much experience from those imaginary cases as i should from real ones, and in addition, i learned a method which is the one that i practise to this day."

"do you mean that you still invent imaginary cases as mental exercises?"

"no; i mean that, when i have a problem of any intricacy, i invent a case which fits the facts and the assumed motives of one of the parties. then i work at that case until i find whether it leads to elucidation or to some fundamental disagreement. in the latter case i reject it and begin the process over again."

"doesn't that method sometimes involve a good deal of wasted time and energy?" i asked.

"no; because each time that you fail to establish a given case, you exclude a particular explanation of the facts and narrow down the field of inquiry. by repeating the process, you are bound, in the end, to arrive at an imaginary case which fits all the facts. then your imaginary case is the real case and the problem is solved. let me recommend you to give the method a trial."

i promised to do so, though with no very lively expectations as to the result, and with this, the subject was allowed, for the present, to drop.