"Yes," assented the Inspector, "it _is_ pretty powerful, and it requires to be so, for it does heavy work and travels a considerable distance. The greater the distance, you know, the greater the power required to do the work and transmit the messages. This is the battery that fires two signal-guns every day at one o'clock--one at Newcastle, the other at South Shields, and supplies Greenwich time to all our principal stations over a radius of three hundred miles.--I sent the contents of one hundred and twenty jars through you just now!" "That's curious and interesting; I may even say it is suggestive," returned the detective, in a meditative tone. "Double that number of jars, now, applied to the locks of street doors at night and the fastenings of windows would give a powerful surprise to burglars." "Ah, no doubt, and also to belated friends," said the Inspector, "not to mention the effect on servant-maids in the morning when people forgot to disconnect the wires." The man in grey admitted the truth of the observation, and, thanking the Battery Inspector for his kind attentions, bade him a cordial adieu. Continuing his investigation of the basement, he came to the three huge fifty-horse-power engines, whose duty it is to suck the air from the pneumatic telegraph tubes in the great hall above. Here the detective became quite an engineer, asked with much interest and intelligence about governors, pistons, escape-valves, actions, etcetera, and wound up with a proposition. "Suppose, now," he said, "that a little dog were to come suddenly into this room and dash about in a miscellaneous sort of way, could it by any means manage to become entangled in your machinery and get so demolished as never more to be seen or heard of?" The engineer looked at his questioner with a somewhat amused expression. "No, sir, I don't think it could. No doubt it might kill itself with much facility in various ways, for fifty horsepower, properly applied, would do for an elephant, much more a dog. But I don't believe that power to be sufficient to produce annihilation. There would have been remains of some sort." From the engine-room our detective proceeded to the boiler-room and the various kitchens, and thence to the basement of the old building on the opposite side of the street, where he found a similarly perplexing labyrinth. He was taken in hand here by Mr Bright, who chanced to be on duty, and led him first to the Stamp Department. There was much to draw him off his "canine" mania here. First he was introduced to the chief of the department, who gave him much interesting information about stamps in general.