He was striking a partition-wall of the “tub,” and perhaps it would be as well for the reader to know how the bottom and the partition-walls of the tub were built. In order to prevent the water surrounding the building-operations from remaining in immediate contact with the walls supporting the whole of the theatrical machinery, the architect was obliged to build a double case in every direction. The work of constructing this double case took a whole year. It was the wall of the first inner case that the Persian struck when speaking to Raoul of the house on the lake. To anyone understanding the architecture of the edifice, the Persian’s action would seem to indicate that Erik’s mysterious house had been built in the double case, formed of a thick wall constructed as an embankment or dam, then of a brick wall, a tremendous layer of cement and another wall several yards in thickness.

At the Persian’s words, Raoul flung himself against the wall and listened eagerly. But he heard nothing⁠ ⁠… nothing⁠ ⁠… except distant steps sounding on the floor of the upper portions of the theater.

The Persian darkened his lantern again.