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Mr. Dillon has lately introduced to the notice of the scientific world, an
improvement upon the _Safety Lamp_ of Sir Humphry Davy, which appears to
us of sufficient interest for illustration in our columns. As the _Davy
Lamp_ is too well known to need special description here, it will be
merely necessary to allude to the principle of the invention, in order to
point out Mr. Dillon's improvement.
He maintains, in opposition to Sir Humphry Davy, that the Davy lamp acts
by its heat and rarefaction, and not from Sir H. Davy's theory, that flame
is cooled by a wire-gauze covering. He shows, by a simple experiment, that
the Davy lamp is not safe in a current of hydrogen or carburetted hydrogen
gas, and that many lives may have been lost from the confidence of miners
in its perfect safety. A current of hydrogen or carburetted hydrogen gas
steadily directed on the flame of the lamp from a bladder and stopcock,
_by cooling the wire gauze_, brings the flame of the lamp through the
gauze to the mouth of the stopcock, (even should there be six folds of
gauze intervening.) He shows also, by immersing the lamp, when cold and
newly lighted, into a jar of dense hydrogen or carburetted hydrogen gas,
or an explosive mixture with atmospheric air, that explosion takes place
inside and outside of the lamp; whereas, when the lamp has burnt
sufficiently long to heat the wire gauze, no explosion takes place on the
outside of the lamp. These experiments appear incontrovertible in support
of his theory, which is, "_that the wire gauze is merely the rapid
receiver and the retainer of heat, and that it is the caloric in its
meshes which prevents the flame of the lamp from being fed by the oxygen
of the atmosphere on the outside_."
The experiments of Libri, showing that flame is inflected by metallic rods,
and that "when two flames are made to approach each other, there is a
mutual repulsion, although their proximity increases the temperature of
each, instead of diminishing it," support Mr. Dillon's theory--the
inflection being occasioned by the rarefaction of the air between the rod
and the flame, the latter seeking for oxygen to support it in a denser
medium, the two flames repelling each other for the same reason, and not
from any mysterious and "repulsive effect of the wires of the gauze
tissue." Mr. Dillon increases the heat of the lamp, and places on it a
shield of talc to protect it from a current, and, upon his theory, the
shafts or workings of iron and coal mines may be lighted with gas with
perfect safety, protecting the flame with wire gauze and a circular shield
of talc.
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