“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.”