9.47. W. by S Granite crossing. Macadam--

and so on. Note every change of direction, with the time; and whenever
you hear or feel anything from outside, note it, with the time and
direction; and don't forget to note any variations in the horse's pace.
You follow the process?"

"Perfectly. But do you think the method is accurate enough to fix the
position of a house? Remember, this is only a pocket-compass with no
dial, and it will jump frightfully. And the mode of estimating distance
is very rough."

"That is all perfectly true," Thorndyke answered. "But you are
overlooking certain important facts The track-chart that you will
produce can be checked by other data. The house, for instance, has a
covered way by which you could identify it if you knew approximately
where to look for it. Then you must remember that your carriage is not
travelling over a featureless plain. It is passing through streets which
have a determined position and direction and which are accurately
represented on the ordnance map. I think, Jervis, that, in spite of the
apparent roughness of the method, if you make your observations
carefully, we shall have no trouble in narrowing down the inquiry to a
quite small area. If we get the chance, that is to say."

"Yes, if we do. I am doubtful whether Mr. Weiss will require my services
again, but I sincerely hope he will. It would be rare sport to locate
his secret burrow, all unsuspected. But now I must really be off."

"Good-bye, then," said Thorndyke, slipping a well-sharpened pencil
through the rubber band that fixed the notebook to the board. "Let me