resently overtook Thorndyke to demand an explanation.

"The stick," said he, "is perfectly simple. The ferrule of a knobbed
stick wears evenly all round; that of a crooked stick wears on one
side--the side opposite the crook. The impressions showed that the
ferrule of this one was evenly convex; therefore it had no crook. The
other matter is more complicated. To begin with, an artificial foot
makes a very characteristic impression, owing to its purely passive
elasticity, as I will show you to-morrow. But an artificial leg fitted
below the knee is quite secure, whereas one fitted above the knee--that
is, with an artificial knee-joint worked by a spring--is much less
reliable. Now, this man had an artificial foot, and he evidently
distrusted his knee-joint, as is shown by his steadying it with his
stick on the same side. If he had merely had a weak leg, he would have
used the stick with his right hand--with the natural swing of the arm,
in fact--unless he had been very lame, which he evidently was not.
Still, it was only a question of probability, though the probability was
very great. Of course, you understand that those particles of woody
fibre and starch granules were disintegrated snuff-grains."

This explanation, like the others, was quite simple when one had heard
it, though it gave me material for much thought as we pedalled on along
the dark road, with Thorndyke's light flickering in front, and the
dogcart pattering in our wake. But there was ample time for reflection;
for our pace rather precluded conversation, and we rode on, mile after
mile, until my legs ached with fatigue. On and on we went through
village after village, now losing the trail in some frequented street,
but picking it up again unfailingly as we emerged on to the country
road, until at last, in the paved High Street of the little town of
Horsefield, we lost it for good. We rode on through the town out on to
the country road; but although there were several tracks of motors,
Thorndyke shook his head at them all. "I have been studying those tyres
until I know them by heart," he said. "No; either he is in the town, or
he has left it by a side road."

There was nothing for it but to put up the horse and the machines at the
hotel, while we walked round to reconnoitre; and this we did, tramping
up one street and down another, with eyes bent on the ground,
fruitlessly searching for a trace of the missing car.

Suddenly, at the door of a blacksmith's