h the arc-flame between their tips. Under these
conditions the arc tends to travel vertically and finally to "stretch"
itself to extinction. However, the arc is kept in place by means of a
magnet above it which repels the arc and holds it at the ends of the
carbons.

The chief objection to the early flame-arcs was the necessity for
frequent renewal of the carbons. This was overcome to a large extent in
the Jandus regenerative lamp in which the arc operates in a glass
enclosure surrounded by an opal globe. However, in addition to the inner
glass enclosure, two cooling chambers of metal are attached to it. Air
enters at the bottom and the fumes from the arc pass upward and into the
cooling chambers, where the solid products are deposited. The air on
returning to the bottom is thus relieved of these solids and the inner
glass enclosure remains fairly clean. The lower carbon is impregnated
with salts for producing the luminous flame and the upper carbon is
cored. The life of the electrodes is about seventy-five hours.

The next step was the introduction of the so-called "luminous-arc" which
is a "flame-arc" with entirely different electrodes. The lower
(negative) electrode consists of an iron tube packed chiefly with
magnetite (an iron oxide) and titanium oxide in the approximate
proportions of three to one respectively. The magnetite is a conductor
of electricity which is easily vaporized. The arc-flame is large and the
titanium gives it a high brilliancy. The positive electrode, usually the
upper one, is a short, thick, solid cylinder of copper, which is
consumed very slowly. This lamp, known as the magnetite-arc, has a
luminous efficiency of about 20 lumens per watt with a clear glass
globe.

The mechanisms which strike the arc and feed the carbons are ingenious
devices of many designs depending upon the kind of arc and upon the
character of the electric circuit to which it is connected. Late
developments in electric incandescent filament lamps have usurped some
of the fields in which the arc-lamp reigned supreme for years and its
future does not appear as bright now as it did ten years ago.
High-intensity arcs have been devised with small carbons for special
purposes and considered as a whole a great amount of ingenuity has been
expended in the development of arc-lamps. There will be a continued
demand for arc-lamps, for scientific developments are opening new fields
for them. Their value in photo-engraving, in the m