onvert the coal instantly
into an intense electric light of dazzling beauty. The point of an
ordinary lead pencil applied in the same way became equally brilliant.

"That must be a powerful battery," remarked the detective.

The Inspector smilingly took two handles from a neighbouring shelf and
held them out to his visitor.

"Lay hold of these," he said, "and you will feel its powers."

The detective did as directed, and received a shock which caused him to
fling down the handles with great promptitude and violence. He was too
self-possessed a man, however, to seem put out.

"Strong!" he said, with a short laugh; "remarkably strong and
effective."

"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 questio