e chart?"

"I will show you," said Thorndyke. "We shall establish the true scale
and that will form part of the proof."

He rapidly constructed on the upper blank part of the paper, a
proportional diagram consisting of two intersecting lines with a single
cross-line.

"This long line," he explained, "is the distance from Stillbury's house
to the Vauxhall railway bridge as it appears on the chart; the shorter
cross-line is the same distance taken from the ordnance map. If our
inference is correct and the chart is reasonably accurate, all the other
distances will show a similar proportion. Let us try some of them. Take
the distance from Vauxhall bridge to the Glasshouse Street bridge."

[Illustration: The Track Chart, showing the route followed by Weiss's
carriage.

A.--Starting-point in Lower Kennington Lane.

B.--Position of Mr. Weiss's house. The dotted lines connecting the
bridges indicate probable railway lines.]

He made the two measurements carefully, and, as the point of the
dividers came down almost precisely in the correct place on the diagram,
he looked up at me.

"Considering the roughness of the method by which the chart was made, I
think that is pretty conclusive, though, if you look at the various
arches that you passed under and see how nearly they appear to follow
the position of the South-Western Railway line, you hardly need further
proof. But I will take a few more proportional measurements for the
satisfaction of proving the case by scientific methods before we proceed
to verify our conclusions by a visit to the spot."

He took off one or two more distances, and on comparing them with the
proportional distances on the ordnance map, found them in every case as
nearly correct as could be expected.

"Yes," said Thorndyke, laying down the dividers, "I think we have
narrowed down the locality of Mr. Weiss's house to a few yards in a
known street. We shall get further help from your note of nine
twenty-three thirty, when records a patch of newly laid macadam
extending up to the house."

"That new macadam will be pretty well smoothed down by now," I objected.

"Not so very completely," answered Thorndyke. "It is only a little over
a month ago, and there has been very little wet weather since. It may be
smooth, but it will be easily distinguishable from the old."

"And do I understand that you propose to go and explore the
neighbourhood?"

"Undoubtedly I do. That is to say, I intend to conve