"Yes. I was thinking that if these embarrassments had been growing up gradually for some time, they might have already assumed an acute form at the time of the robbery."
"That is well considered," said my colleague. "But what is the special bearing on the case supposing it was so?"
"On the supposition," I replied, "that 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, laughing.