The life of George Stephenson, railway engineer - Lighthouse ...

CHAP. XI.] THE TUBE LAMP.
129
appears that Mr. Smithson Tennant and Dr. WoUaston had
observed the same fact several years before,* though neither
Stephenson nor Davy knew it while they were prosecuting their
experiments. Sir Humphry Davy's subsequent modification of
the tube lamp, by which, while diminishing the diameter, he in
the same ratio shortened the tubes without danger, and in the
form of wire-gauze enveloped the safety lamp by a multiplicity
of tubes, was a beautiful application of the true theory which he
had formed upon the subject. " The whole theory and operation
of the safety lamp," says Davy's biographer,! " is nothing more
than an apparatus by which the inflammable air, upon exploding
in its interior, cannot pass out without being so far cooled, as to
deprive it of the power of communicating inflammation to the
surrounding atmosphere. The principle having been once dis-
covered, it was easy to adopt and multiply practical applications
of it. From the result of these researches it became evident,
that to light mines infested with fire-damp, with perfect security,
it was only necessary to use an air-tight lanthorn, supplied with
air from tubes of small diameter, through which explosions cannot
pass,^and with a chimney on a similar principle at the upper part
to carry off the foul air. A common lanthorn, to be adapted to
theipurpose, merely required to be made air-tight in the door
and sides, and to be furnished with a chimney, and the system
of safety apertures below and above the flame of the lamp.
Such, in fact, was Davy's first safety lamp ; and having after-
wards varied the arrangements of the tubes in different ways, he
at length exchanged them for canals, which consisted of close
concentric hollow metallic cylinders of different diameters, so
placed together as to form circular canals of the diameter of from
one twenty-fifth to one fortieth of an inch, and of an inch and
seven tenths in length." Carrying out the same principle, the
idea occurred to him of constructing the lamp entirely of wire-
gauze, with apertures of from one fortieth to one sixtieth of an
inch in diameter. A lamp so constructed was exhibited in
January, 1816, and shortly after came into general use.
* Paris's Life of Davy, 4to. ed., p. 316, and note to Davy's Paper read before
the Eoyal Society, November 9th, 1815.
t Paris's Life of Davy, 4to. ed. , p. 317.
6 *