reaches the flame. Moreover, the tin
shield lamp, when inclined to one side, is extinguished (though not so
easily as the Mueseler); and as the inlet holes are 6 inches from the top,
it does not show a thin stratum of fire-damp near the roof as perceptibly
as the Davy, which admits of being put in almost a horizontal position.
Although the Davy lamp was, nearly fifty years ago, pronounced unsafe, by
reason of its inability to resist an ordinary velocity of eight feet per
second, yet it is still kept in use on account of its sensitiveness. Its
advocates maintain that a mine can be kept safer by using the Davy, which
detects small quantities of gas, and thereby shows the real state of the
mine, than by a lamp which, though able to resist a greater velocity, is
not so sensitive, and consequently is apt to deceive. Assuming the Davy
lamp to be condemned (as it has already been in Belgium and in some English
mines), the Stephenson and some of the more recently invented lamps
pronounced unsafe, then if greater shielding is recommended the question
is, what means have we for detecting small quantities of fire-damp?

It would seem from the foregoing remarks that in any existing safety-lamp,
where one qualification is increased another is proportionately reduced; so
it is doubtful whether all the necessary requirements of sensitiveness,
resistance to strong currents, satisfactory light, self-extinction, perfect
combustion, etc., can ever be combined in one lamp. The object of the
present paper is to show that with the assistance of the fire-damp
detecter, the tin shield, or any other description of lamp, is made as
sensitive as the Davy, while its other advantages of resisting velocity,
etc., are not in any way interfered with. As a proof of this I may mention
that a deputy of experience recently visited a working place to make his
inspection. He reported the stall to be free from gas, but when the manager
and steward visited it with the detecter, which they applied to the roof
(where it would have been difficult to put even a small Davy), it drew a
sample of the atmosphere which, on being put to the test tube in the
tin-shield lamp, at once showed the presence of fire-damp. Out of
twenty-eight tests in a mine working a long-wall face the Davy showed gas
only eleven times, while the detecter showed it in every case. The
detecter, as will be perceived from the one exhibited, and the accompanying
sectional drawing, consists simply