"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