“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.”

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 Southwestern 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.”