The Red Thumb Mark. Richard Austin Freeman

But you will understand when you see me use the instrument, and remember, you are to make no comments."

      We had by this time arrived at the entrance to Scotland Yard, and were passing up the narrow thoroughfare, when we encountered a uniformed official who halted and saluted my colleague.

      "Ah, I thought we should see you here before long, doctor," said he genially. "I heard this morning that you have this thumb-print case in hand."

      "Yes," replied Thorndyke; "I am going to see what can be done for the defence."

      "Well," said the officer as he ushered us into the building, "you've given us a good many surprises, but you'll give us a bigger one if you can make anything of this. It's a foregone conclusion, I should say."

      "My dear fellow," said Thorndyke, "there is no such thing. You mean that there is a prima facie case against the accused."

      "Put it that way if you like," replied the officer, with a sly smile, "but I think you will find this about the hardest nut you ever tried your teeth on—and they're pretty strong teeth too, I'll say that. You had better come into Mr. Singleton's office," and he conducted us along a corridor and into a large, barely-furnished room, where we found a sedate-looking gentleman seated at a large writing table.

      "How-d'ye-do, doctor?" said the latter, rising and holding out his hand. "I can guess what you've come for. Want to see that thumb-print, eh?"

      "Quite right," answered Thorndyke, and then, having introduced me, he continued: "We were partners in the last game, but we are on opposite sides of the board this time."

      "Yes," agreed Mr. Singleton; "and we are going to give you check-mate."

      He unlocked a drawer and drew forth a small portfolio, from which he extracted a piece of paper which he laid on the table. It appeared to be a sheet torn from a perforated memorandum block, and bore the pencilled inscription: "Handed in by Reuben at 7.3 p.m., 9.3.01. J. H." At one end was a dark, glossy blood-stain, made by the falling of a good-sized drop, and this was smeared slightly, apparently by a finger or thumb having been pressed on it. Near to it were two or three smaller smears and a remarkably distinct and clean print of a thumb.

      Thorndyke gazed intently at the paper for a minute or two, scrutinising the thumb-print and the smears in turn, but making no remark, while Mr. Singleton watched his impassive face with expectant curiosity.

      "Not much difficulty in identifying that mark," the official at length observed.

      "No," agreed Thorndyke; "it is an excellent impression and a very distinctive pattern, even without the scar."

      "Yes," rejoined Mr. Singleton; "the scar makes it absolutely conclusive. You have a print with you, I suppose?"

      "Yes," replied Thorndyke, and he drew from a wide flap-pocket the enlarged photograph, at the sight of which Mr. Singleton's face broadened into a smile.

      "You don't want to put on spectacles to look at that," he remarked; "not that you gain anything by so much enlargement; three diameters is ample for studying the ridge-patterns. I see you have divided it up into numbered squares—not a bad plan; but ours—or rather Galton's, for we borrowed the method from him—is better for this purpose."

      He drew from the portfolio a half-plate photograph of the thumb-print which appeared magnified to about four inches in length. The print was marked by a number of figures written minutely with a fine-pointed pen, each figure being placed on an "island," a loop, a bifurcation or some other striking and characteristic portion of the ridge-pattern.

      "This system of marking with reference numbers," said Mr. Singleton, "is better than your method of squares, because the numbers are only placed at points which are important for comparison, whereas your squares or the intersections of the lines fall arbitrarily on important or unimportant points according to chance. Besides, we can't let you mark our original, you know, though, of course, we can give you a photograph, which will do as well."

      "I was going to ask you to let me take a photograph presently," said Thorndyke.

      "Certainly," replied Mr. Singleton, "if you would rather have one of your own taking. I know you don't care to take anything on trust. And now I must get on with my work, if you will excuse me. Inspector Johnson will give you any assistance you may require."

      "And see that I don't pocket the original," added Thorndyke, with a smile at the inspector who had shown us in.

      "Oh, I'll see to that," said the latter, grinning; and, as Mr. Singleton returned to his table, Thorndyke unlocked the microscope case and drew forth the instrument.

      "What, are you going to put it under the microscope?" exclaimed Mr. Singleton, looking round with a broad smile.

      "Must do something for my fee, you know," replied Thorndyke, as he set up the microscope and screwed on two extra objectives to the triple nose-piece.

      "You observe that there is no deception," he added to the inspector, as he took the paper from Mr. Singleton's table and placed it between two slips of glass.

      "I'm watching you, sir," replied the officer, with a chuckle; and he did watch, with close attention and great interest, while Thorndyke laid the glass slips on the microscope stage and proceeded to focus.

      I also watched, and was a good deal exercised in my mind by my colleague's proceedings. After a preliminary glance with the six-inch glass, he swung round the nose-piece to the half-inch objective and slipped in a more powerful eye-piece, and with this power he examined the blood-stains carefully, and then moved the thumb-print into the field of vision. After looking at this for some time with deep attention, he drew from the case a tiny spirit lamp which was evidently filled with an alcoholic solution of some sodium salt, for when he lit it I recognised the characteristic yellow sodium flame. Then he replaced one of the objectives by a spectroscopic attachment, and having placed the little lamp close to the microscope mirror, adjusted the spectroscope. Evidently my friend was fixing the position of the "D" line (or sodium line) in the spectrum.

      Having completed the adjustments, he now examined afresh the blood-smears and the thumb-print, both by transmitted and reflected light, and I observed him hurriedly draw one or two diagrams in his notebook. Then he replaced the spectroscope and lamp in the case and brought forth the micrometer—a slip of rather thin glass about three inches by one and a half—which he laid over the thumb-print in the place of the upper plate of glass.

      Having secured it in position by the clips, he moved it about, comparing its appearance with that of the lines on the large photograph, which he held in his hand. After a considerable amount of adjustment and readjustment, he appeared to be satisfied, for he remarked to me—

      "I think I have got the lines in the same position as they are on our print, so, with Inspector Johnson's assistance, we will take a photograph which we can examine at our leisure."

      He extracted the camera—a quarter-plate instrument—from its case and opened it. Then, having swung the microscope on its stand into a horizontal position, he produced from the camera case a slab of mahogany with three brass feet, on which he placed the camera, and which brought the latter to a level with the eye-piece of the microscope.

      The front of the camera was fitted with a short sleeve of thin black leather, and into this the eye-piece end of the microscope was now passed, the sleeve being secured round the barrel of the microscope by a stout indiarubber band, thus producing a completely light-tight connection.

      Everything was now ready for taking the photograph. The light from the window having been concentrated on the thumb-print by means of a condenser, Thorndyke proceeded to focus the image on the ground-glass screen with extreme care and then, slipping a small leather cap over the objective, introduced the dark slide and drew out the shutter.

      "I will ask you to sit down and remain quite still while I make the exposure," he said to me and the inspector. "A very little vibration is enough to destroy the sharpness of the image."

      We seated ourselves accordingly, and Thorndyke then removed the cap, standing motionless, watch in hand, while he exposed the first plate.

      "We may as well take a second, in case this should not turn out quite perfect," he said, as he replaced the cap and closed the shutter.

      He