air-currents containing methane in dangerous proportions striking the
lamps at different angles, and the relative safety of the various types
of lamps under such conditions can be determined. In this gallery it is
also possible to test lighting devices either in a quiet atmosphere or
in a moving current, and, by subjecting the lamps to air containing
known percentages of methane, it is possible to acquaint the user with
the appearance of the flame caps.

Breathing Apparatus.

With this apparatus, the wearer may explore a gaseous mine, approach
fires for the purpose of fighting them, or make investigations after an
explosion. Its object is to provide air or oxygen to be breathed by the
wearer in coal mines, when the mine air is so full of poisonous gases as
to render life in its presence impossible.

A variety of forms of rescue helmets and apparatus are on the market,
almost all of European manufacture, which are being subjected to
comparative trials as to their durability and safety, the ease or
inconvenience involved in their use, etc. All consist essentially of
helmets which fit air-tight about the head, or of air-tight nose clamps
and mouthpieces (Fig. 1, Plate XII).

These several forms of breathing apparatus are of three types:

1.--The liquid-air type, in which air, in a liquid state, evaporates and
provides a constant supply of fresh air.

2.--The chemical oxygen-producing type, which artificially makes or
supplies oxygen for breathing at about the rate required; and,