f the tip of the flame. However, the gauze
reduces the luminous output, and as it accumulates soot and dust the
light is greatly diminished. One of these lamps is about as luminous as
a candle, initially, but its intensity is often reduced by accumulations
upon the gauze to only one fifth of the initial value.

The acetylene lamp is the best open-flame light-source available to the
miner, for several reasons. It is of a higher candle-power than the
others and as it is a burning gas, there is not the danger of flying
sparks as in the case of burning wicks. The greater intensity of
illumination affords a greater safety to the miner by enabling him to
detect loose rock which may be ready to fall upon him. However, this
lamp may be a source of danger, owing to the fact that it will burn more
brilliantly in a vitiated atmosphere than other flame-lamps. Another
disadvantage is the possibility of calcium carbide accidentally spilt
coming in contact with water and thereby causing the generation of
acetylene gas. If this is produced in the mine in sufficient quantities
it is a danger which may not be suspected. If ignited it will explode
and may also cause severe burns.

The electric lamp, being an enclosed light-source capable of being
subdivided and fed by a small portable battery, early gave promise of
solving the problem of a safe mine-lamp of adequate candle-power. Much
ingenuity has been applied to the development of a portable electric
safety mine-lamp, and several such lamps are now approved by the Bureau
of Mines. Two general types are being manufactured, the cap outfit and
the hand outfit. They consist essentially of a lamp in a reflector whose
aperture is closed with a sheet or a lens of clear glass. The battery
may be of the "dry" or "storage" type and in the case of the cap outfit
the battery is carried on the back. The specifications for these lamps
demand that a luminous intensity averaging at least 0.4 candle be
maintained throughout twelve consecutive hours of operation. At no time
during this period shall the output of light fall below 1.25 lumens for
a cap-lamp and below 3 lumens for a hand-lamp. Inasmuch as these are
equipped with reflectors, the specifications insist that a circle of
light at least seven feet in diameter shall be cast on a wall twenty
inches away. It appears that a portable lamp is an economic necessity in
the coal-mines, on account of the expense, inconvenience, and possible
dangers introd