By the illustration of a gas globule, which is ignited from a spark by
induction, Mr. Faraday has proved in a most interesting manner that the
corrugated-iron roofs of some gunpowder-magazines,--on the subject of
which he had often been consulted by the builders, with a view to the
greater safety of these manufactories,--are absolutely dangerous by the
laws of induction; as, by the return of induction, while a storm was
discharging itself a mile or two off, a secondary spark might ignite
the building.