“What’s the matter with the mill?” he inquired.
“The stamps have been ‘hung up’ for an hour,” answered Burke, “so the amalgamators can dress down the plates.”
“It happens twice in every twenty-four hours,” put in Mr. Bradlaugh, “once on the night shift and once while the day men are on duty. We——”
Sim, who had started back to his work in the mill, returned and thrust his head in at the door just at that moment.
“Something queer goin’ on among the tanks, Burke,” he reported.
“Something queer, Sim?” echoed the super. “What do you mean by that?”
“Step outside once an’ use your ears.”
Not only Burke, but all the others, stepped from the laboratory building and stood at attention, facing the grim, black tanks. Thump, thump thump! came a hollow, reverberating note. There was nothing else, merely that thump, thump, thump! It came sometimes at regular intervals and sometimes a bit wildly and uncertainly.
“What is it?” inquired Mr. Bradlaugh.
“Blest if I can sabe it,” said Sim.