ults in a
mantle superior to previous mantles in strength, flexibility, permanence
of form, and permanence of luminous property. This artificial silk
mantle will permit of handling even after it has been in use for several
hundred hours. This great advance appears to be due to the fact that
after the artificial-silk fibers have been burned off, the fibers are
solid and continuous instead of porous as in previous mantles.

The color-value of the light from mantles may be varied considerably by
altering the proportions of the rare-earths. The yellowness of the light
has been traced to ceria, so by varying the proportions of ceria, the
color of the light may be influenced.

The inverted mantle introduced greater possibilities into gas-lighting.
The light could be directed downward with ease and many units such as
inverted bowls were developed. In fact, the lighting-fixtures and the
lighting-effects obtainable kept pace with those of electric lighting,
notwithstanding the greater difficulties encountered by the designer of
gas-lighting fixtures. Many problems were encountered in designing an
inverted burner operating on the Bunsen principle, but they were finally
satisfactorily solved. In recent years a great deal of study has been
given to the efficiency of gas-burners, with the result that a high
level of development has been reached.

Several methods of electrical ignition have been evolved which in
general employ the electric spark. Electrical ignition and developments
of remote control have added great improvements especially to
street-lighting by means of gas. Gas-valves for remote control are
actuated by gas pressure and by electromagnets. In general, the
gas-lighting engineers have kept pace marvelously with electric
lighting, when their handicaps are considered.

Various types of burners have appeared which aimed to burn more gas in a
given time under a mantle and thereby to increase the output of light.
These led to the development of the pressure system in which the
pressure of gas was at first several times greater than usual. The gas
is fed into the mixing tube under this higher pressure in a manner which
also draws in an adequate amount of air. In this way the combustion at
the burner is forced beyond the point reached with the usual pressure.
Ordinary gas pressure is equal to that of a few inches of water, but
high-pressure systems employ pressures as great as sixty inches of
water. Under this high-pressu