ding to the Bureau of Mines during the
years 1916 and 1917 about 60 per cent. of the fatalities due to gas and
coal-dust explosions were directly traceable to the use of defective
safety lamps and to open flames.

In the early days of coal-mining it was found that the flame of a candle
occasionally caused explosions in the mines. It was also found that
sparks of flint and steel would not readily ignite the gas or coal-dust
and this primitive device was used as a light-source. Of course,
statistics are unavailable concerning the casualties in coal-mines
throughout the past centuries, but with the accidents not uncommon in
this scientific age, with its elaborate organizations striving to stamp
out such casualties, there is good reason to believe that previous to a
century or two ago the risks of coal-mining must have been great. Open
flames have been widely used in this industry, but there has always been
the risk of the presence or the appearance of gas or explosive dust.

The early open-flame lamps not only were sources of danger but their
feeble varying intensity caused serious damage to the eyesight of
miners. This factor is always present in inadequate and improper
lighting, but its influence is noticeable in coal-mining in the nervous
disease affecting the eyes which is known as nystagmus. The symptoms of
the disease are inability to see at night and the dazzling effect of
ordinary lamps. Finally objects appear to the sufferer to dance about
and his vision is generally very much disturbed.

The oil-lamps used in coal-mining have a luminous intensity equivalent
to about one to four candles, but owing to the atmospheric conditions in
the mines a flame does not burn as brightly as in the fresh air. The
possibility of explosion due to the open flame was eliminated by
surrounding it with a metal gauze. Davy was the inventor of this device
and his safety lamp introduced about a hundred years ago has been a boon
to the coal-miner. Various improvements have been devised, but Davy's
lamp contained the essentials of a safety device. The flame is
surrounded by a cylinder of metal gauze which by forming a much cooler
boundary prevents the mine-gas from becoming heated locally by the lamp
flame to a sufficient temperature to ignite and consequently to explode.
This device not only keeps the flame from igniting the gas but it also
serves as an indicator of the amount of gas present, by the variation in
the size and appearance o