The Sign of the Four | Page 5

it I enumerate a hundred and
forty forms of cigar-, cigarette-, and pipe-tobacco, with colored plates illustrating the
difference in the ash. It is a point which is continually turning up in criminal trials, and
which is sometimes of supreme importance as a clue. If you can say definitely, for
example, that some murder has been done by a man who was smoking an Indian lunkah,
it obviously narrows your field of search. To the trained eye there is as much difference
between the black ash of a Trichinopoly and the white fluff of bird's-eye as there is
between a cabbage and a potato."

"You have an extraordinary genius for minutiae," I remarked.
"I appreciate their importance. Here is my monograph upon the tracing of footsteps, with
some remarks upon the uses of plaster of Paris as a preserver of impresses. Here, too, is a
curious little work upon the influence of a trade upon the form of the hand, with
lithotypes of the hands of slaters, sailors, corkcutters, compositors, weavers, and
diamond-polishers. That is a matter of great practical interest to the scientific
detective,--especially in cases of unclaimed bodies, or in discovering the antecedents of
criminals. But I weary you with my hobby."
"Not at all," I answered, earnestly. "It is of the greatest interest to me, especially since I
have had the opportunity of observing your practical application of it. But you spoke just
now of observation and deduction. Surely the one to some extent implies the other."
"Why, hardly," he answered, leaning back luxuriously in his arm- chair, and sending up
thick blue wreaths from his pipe. "For example, observation shows me that you have
been to the Wigmore Street Post-Office this morning, but deduction lets me know that
when there you dispatched a telegram."
"Right!" said I. "Right on both points! But I confess that I don't see how you arrived at it.
It was a sudden impulse upon my part, and I have mentioned it to no one."
"It is simplicity itself," he remarked, chuckling at my surprise,--"so absurdly simple that
an explanation is superfluous; and yet it may serve to define the limits of observation and
of deduction. Observation tells me that you have a little reddish mould adhering to your
instep. Just opposite the Seymour Street Office they have taken up the pavement and
thrown up some earth which lies in such a way that it is difficult to avoid treading in it in
entering. The earth is of this peculiar reddish tint which is found, as far as I know,
nowhere else in the neighborhood. So much is observation. The rest is deduction."
"How, then, did you deduce the telegram?"
"Why, of course I knew that you had not written a letter, since I sat opposite to you all
morning. I see also in your open desk there that you have a sheet of stamps and a thick
bundle of post- cards. What could you go into the post-office for, then, but to send a wire?
Eliminate all other factors, and the one which remains must be the truth."
"In this case it certainly is so," I replied, after a little thought. "The thing, however, is, as
you say, of the simplest. Would yo think me impertinent if I were to put your theories to a
more severe test?"
"On the contrary," he answered, "it would prevent me from taking a second dose of
cocaine. I should be delighted to look into any problem which you might submit to me."
"I have heard you say that it is difficult for a man to have any object in daily use without
leaving the impress of his individuality upon it in such a way that a trained observer
might read it. Now, I have here a watch which has recently come into my possession.
Would you have the kindness to let me have an opinion upon the character or habits of

the late owner?"
I handed him over the watch with some slight feeling of amusement in my heart, for the
test was, as I thought, an impossible one, and I intended it as a lesson against the
somewhat dogmatic tone which he occasionally assumed. He balanced the watch in his
hand, gazed hard at the dial, opened the back, and examined the works, first with his
naked eyes and then with a powerful convex lens. I could hardly keep from smiling at his
crestfallen face when he finally snapped the case to and handed it back.
"There are hardly any data," he remarked. "The watch has been recently cleaned, which
robs me of my most suggestive facts."
"You are right," I answered. "It was cleaned before being sent to me." In my heart I
accused my companion of putting forward a most lame and impotent