This could rarely be compassed in real life, but it is, of course, easy for the author to provide the tiny clues necessary to his hero's microscope work.
And tiny clues are a favorite device of the detective story writer. There is a fascination about the solving of a big murder mystery by a bit of a broken cuff-link; or the tracing of a professional burglar by a speck of cigarette ash. Of course, the philosophy is that these dues are so small as to be unnoticed by the criminal who so conveniently leaves them behind him. Also they are unnoticed by the amateur or the Central Office sleuth, and so redound to the glory of the Transcendent Detective.
But most of all their use is to impress and astound the reader by a picturesque application of the truth that great oaks from little acorns grow.
It is the dramatic contrast of the tiny indication that points the way to the enormous result of discovering the perpetrator of an atrocious crime.
But here again we have the great gulf fixed between the Real Detective and the Fiction Detective. Take the vital point in "File No. 113." Now really there is not one chance in a thousand that the particle of green paint would have been found adhering to that key, had the key been found. Green paint will adhere most annoyingly to clothing, or hands, or even keys when it is not desired, but if needed as criminal evidence it will in all probability be found wanting.
But the field of fiction is as a salted mine. What is searched for is found, and the detective triumphantly ferrets out the infinitesimal clues that have been most carefully put in place by the author.
When Sherlock Holmes looked for a burnt match in "Silver Blaze," he found it, though the really careful inspector had carefully overlooked it. This is the account of the scene:
> "My dear Inspector, you surpass yourself!" Holmes took the bag, and, descending into the hollow, he pushed the matting into a more central position. Then stretching himself upon his face and leaning his chin upon his hands, he made a careful study of the trampled mud in front of him. "Hullo!"
said he, suddenly. "What's this?" It was a wax vesta half burned, which was so coated with mud that it looked at first like a little chip of wood.
> "I cannot think how I came to overlook it," said the Inspector, with an expression of annoyance.
> "It was invisible, buried in the mud. I only saw it because I was looking for it."
> "What! you expected to find it?"
> "I thought it not unlikely."
> This is a fine instance of spectacular detective work. And this is what is demanded for the true technique of the Mystery Story. It is not real life; it is a stage, set with the furnishings and properties of the dramatic plot. The dropped handkerchiefs, the shreds of cloth or torn bits of paper, are carefully placed, and the detective has only to step along and pick them up.
> Wilkie Collins' creation, Sergeant Cuff, sanctions it emphatically:
> "I made a private inquiry last week, Mr. Superintendent," he said. "At one end of the inquiry there was a murder, and at the other end there was a spot of ink on a table-cloth that nobody could account for. In all my experience along the dirtiest ways of this dirty little world I have never met with such a thing as a trifle yet."
A case in point, is this bit from "The Whispering Man:"
> "I turned to go. Just as I did so, my eye caught a glint from the carpet, of what I took to be a bent pin. Quite automatically—for by nature I am an orderly and methodical person—I stooped and picked it up. It was not a pin after all, but the broken end of a curved needle. It made no particular impression on my mind, and I was on the point of dropping it into the waste- paper basket when something stopped me. It was no very definite idea, probably just a reminiscence from detective stories I had read, of the immense importance of the most trivial things."
It was this that Lowell had in mind, when he said that Poe "combined in a very remarkable manner two faculties which are seldom found united,—a power of influencing the mind of the reader by the impalpable shadows of mystery, and a minuteness of detail which does not leave a pin or a button unnoticed. Both are, in truth, the natural results of the predominating quality of his mind, to which we have before alluded,—analysis." And the same principle is approved of in real life by Mr. Arthur C. Train's assertion: "The discovery and proper proof of minute facts which tend to demonstrate the guilt of an accused are the joy of the natural prosecutor, and he may in his enthusiasm spend many thousands of dollars on what seems, and often is, an immaterial matter."