he three
qualities necessary for the ideal detective. He has the power of
observation and that of deduction. He is only wanting in knowledge;
and that may come in time. He is now translating my small works into
French."

"Your works?"

"Oh, didn't you know?" he cried, laughing. "Yes, I have been guilty of
several monographs. They are all upon technical subjects. Here, for
example, is one 'Upon the Distinction between the Ashes of the Various
Tobaccoes.' In 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