at Mr. Hornby was in actual
pecuniary difficulties at the date of the robbery, it seems to me
possible to construct a hypothesis as to the identity of the robber."

"I should like to hear that hypothesis stated," said Thorndyke, rousing
himself and regarding me with lively interest.

"It is a highly improbable one," I began with some natural shyness at
the idea of airing my wits before this master of inductive method; "in
fact, it is almost fantastic."

"Never mind that," said he. "A sound thinker gives equal consideration
to the probable and the improbable."

Thus encouraged, I proceeded to set forth the theory of the crime as it
had occurred to me on my way home in the fog, and I was gratified to
observe the close attention with which Thorndyke listened, and his
little nods of approval at each point that I made.

When I had finished, he remained silent for some time, looking
thoughtfully into the fire and evidently considering how my theory and
the new facts on which it was based would fit in with the rest of the
data. At length he spoke, without, however, removing his eyes from the
red embers--

"This theory of yours, Jervis, does great credit to your ingenuity. We
may disregard the improbability, seeing that the alternative theories
are almost equally improbable, and the fact that emerges, and that
gratifies me more than I can tell you, is that you are gifted with
enough scientific imagination to construct a possible train of events.
Indeed, the improbability--combined, of course, with possibility--really
adds to the achievement, for the dullest mind can perceive the
obvious--as, for instance, the importance of a finger-print. You have
really done a great thing, and I congratulate you; for you have
emancipated yourself, at least to some extent, from the great
finger-print obsession, which has possessed the legal mind ever since
Galton published his epoch-making monograph. In that work I remember he
states that a finger-print affords evidence requiring no
corroboration--a most dangerous and misleading statement which has been
fastened upon eagerly by the police, who have naturally been delighted
at obtaining a sort of magic touchstone by which they are saved the
labour of investigation. But there is no such thing as a single fact
that 'affords evidence requiring no corroboration.' As well might one
expect to make a syllogism with a single premise." "I suppose they
would hardly go so far as that," I said, laug