orth of England, and visiting some of the
principal collieries in the neighbourhood of Newcastle, soon convinced
himself that no improvement could be made in the mode of ventilation, but
that the desired preventive must be sought in a new method of lighting
the mines, free from danger, and which, by indicating the state of the
air in the part of the mine where inflammable air was disengaged, so as
to render the atmosphere explosive, should oblige the miners to retire
till the workings were properly cleared. The common means then employed
for lighting the dangerous part of the mines consisted of a steel wheel
revolving in contact with flint, and affording a succession of sparks:
but this apparatus always required a person to work it, and was not
entirely free from danger. The fire-damp was known to be light
carburetted hydrogen gas; but its relations to combustion had not been
examined. It is chiefly produced from what are called blowers or fissures
in the broken strata, near dykes. Sir Humphry made various experiments on
its combustibility and explosive nature; and discovered, that the
fire-damp requires a very strong heat for its inflammation; that azote and
carbonic acid, even in very small proportions, diminished the velocity of
the inflammation; that mixtures of the gas would not explode in metallic
canals or troughs, where their diameter was less than one-seventh of an
inch, and their depth considerable in proportion to their diameter; and
that explosions could not be made to pass through such canals, or through
very fine wire sieves, or wire gauze. The consideration of these facts
led Sir Humphry to adopt a lamp, in which the flame, by being supplied
with only a limited quantity of air should produce such a quantity of
azote and carbonic acid as to prevent the explosion of the fire-damp, and
which, by the nature of its apertures for giving admittance and egress to
the air, should be rendered incapable of communicating any explosion to
the external air. These requisites were found to be afforded by air-tight
lanterns, of various constructions, supplied with air from tubes or
canals of small diameter, or from apertures covered with wire-gauze,
placed below the flame, through which explosions cannot be communicated;
and having a chimney at the upper part, for carrying off the foul air.
Sir Humphry soon afterwards found that a constant flame might be kept up
from the explosive mixture issuing from the apertures of a wire