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."