“H’m,” grunted Thorndyke, as he sauntered up and down the room, teacup in hand, “to guess, eh?  I like not that word ‘guess’ in the mouth of a man of science.  What do you mean by a ’guess’?”

His manner was wholly facetious, but I professed to take his question seriously, and replied—­

“By a guess, I mean a conclusion arrived at without data.”

“Impossible!” he exclaimed, with mock sternness.  “Nobody but an utter fool arrives at a conclusion without data.”

“Then I must revise my definition instantly,” I rejoined.  “Let us say that a guess is a conclusion drawn from insufficient facts.”

“That is better,” said he; “but perhaps it would be better still to say that a guess is a particular and definite conclusion deduced from facts which properly yield only a general and indefinite one.  Let us take an instance,” he continued.  “Looking out of the window, I see a man walking round Paper Buildings.  Now suppose I say, after the fashion of the inspired detective of the romances, ’That man is a stationmaster or inspector,’ that would be a guess.  The observed facts do not yield the conclusion, though they do warrant a conclusion less definite and more general.”

“You’d have been right though, sir!” exclaimed Polton, who had stepped forward with me to examine the unconscious subject of the demonstration.  “That gent used to be the stationmaster at Camberwell.  I remember him well.”  The little man was evidently greatly impressed.

“I happen to be right, you see,” said Thorndyke; “but I might as easily have been wrong.”

“You weren’t though, sir,” said Polton.  “You spotted him at a glance.”

In his admiration of the result he cared not a fig for the correctness of the means by which it had been attained.

“Now why do I suggest that he is a stationmaster?” pursued Thorndyke, disregarding his assistant’s comment.

“I suppose you were looking at his feet,” I answered.  “I seem to have noticed that peculiar, splay-footed gait in stationmasters, now that you mention it.”

“Quite so.  The arch of the foot has given way; the plantar ligaments have become stretched and the deep calf muscles weakened.  Then, since bending of the weakened arch causes discomfort, the feet have become turned outwards, by which the bending of the foot is reduced to a minimum; and as the left foot is the more flattened, so it is turned out more than the right.  Then the turning out of the toes causes the legs to splay outward from the knees downwards—­a very conspicuous condition in a tall man like this one—­and you notice that the left leg splays out more than the other.