When it becomes a question of practical lighting, it is very certain
that the best electric lamp will be the one that is most simple and
requires the fewest mechanical parts. It is to such simplicity that is
due all the success of the Jablochkoff candle and the Reynier-Werdermann
lamp. Yet, in the former of these lamps, it is to be regretted that the
somewhat great and variable resistance opposed to the current in its
passage through two carbons that keep diminishing in length, in measure
as they burn, proves a cause of loss of light and of variation in it.
And it is also to be regretted that the duration of combustion of the
carbons is not longer; and, finally, it is allowable to believe that the
power employed in volatilizing the insulator placed between the carbons
is prejudicial to the economical use of this system. In order to obviate
this latter inconvenience, an endeavor has been made in the Wilde candle
to do away with the insulator, but the results obtained have scarcely
been encouraging. An endeavor has also been made to render the duration
of the carbons greater by employing quite long ones, and causing these
to move forward successively through the intermedium of a species
of rollers, or of counterpoises, as in the lamps of Mersanne and
Werdermann; but then the system becomes more complicated. Finally, in
order to keep the resistance of the carbons at a minimum and constant,
their contact with the rheophores of the circuit has been established
at a short distance from the arc, and this is one of the principal
advantages possessed by the Reynier-Werdermann system. At a certain
epoch it was thought that the problem might be simply solved by
arranging in front of each other two carbons actuated by a spiral
spring, as in car lamps, and kept at a proper distance apart for forming
the electric arc by two funnel-shaped pieces of calcined magnesia, into
which they entered like a wedge in measure as their conical point were
away through combustion. This was the system of Mr. De Baillehache,
and the trials that were made therewith were very satisfactory. But,
unfortunately, the magnesia was not able to resist very long the
temperature to which it was submitted. The problem found a better
solution in the sun-lamp but has been solved in another manner, and just
as simply, by Mr. Solignac, and the results obtained by him have been
very satisfactory as regarded from the standpoint of steadiness of the
luminous point.
In this system, a general view of which is given in Fig. 1, and the
arrangement in Figs. 2 and 3, the carbons, F F, which are horizontal and
about fifty centimeters in length, are thrust toward each other by
two barrels, K, K, which wind up two chains, E, E, passing around the
pulleys, D, D, fitted to the extremities of the carbons. These latter
are provided beneath with small glass rods, G, G, whose extremities
toward the arc abut at a short distance from the latter against a nickel
stop, L (Fig. 3), which supports them, moreover, at M, by means of
a tappet whose position is regulated by a screw. The current is
transmitted to the carbons by two friction rollers, I, I, which serve at
the same time as a guide for them, and which give the electric flux a
passage of only one or two centimeters over the front of the carbon
to form the arc. Finally, the whole is held by a support, A, and two
pieces, CB, CB, which at the same time lead the current to the friction
rollers through projections, J. The two systems are made to approach
or recede from each other, in order to form the arc, by means of a
regulating screw, H.
At present, the lighting of these lamps is effected by means of this
screw, H, but Mr. Solignac is now constructing a model in which the
lighting will be performed automatically by means of a solenoid that
will react upon a carbon lighter, as in several already well known
systems.
[Illustration: Fig. 1]
If the preceding description has been well-understood, it will be seen
that the carbons are arrested in their movement toward each other only
by the glass rods, G, abutting against L; but, as the stops, L, are not
far from the arc, and as the heat to which they are exposed is so much
the greater in proportion as the incandescent part of the carbons is
nearer them, it results that for a certain elongation of the arc the
temperature becomes sufficient to soften the glass of the rods, G, G,
so that they bend as shown at O (Fig. 3), and allow the carbons to move
onward until the heat has sufficiently diminished to prevent any further
softening of the glass. In measure as the wearing away progresses, the
preceding effects are reproduced; and, as these are produced in an
imperceptible and continuous manner, there is perceived no jumping nor
inconstancy in the light of the arc. Under such conditions, then, the
regulation of the arc is effected under the very influence of the
effect produced; and not under that of an action of a different nature
(electro-magnetism), as happens in other regulators. It is certain that
this idea is new and original, and the results that we have witnessed
from it have been very satisfactory. There is but one regulation to
perform, and that at the beginning, but this once done the apparatus
operates with certainty, and for a long time. With a Meritens machine of
the first model it has been found possible to light five lamps of this
kind placed in the same circuit.
[Illustration: Fig. 2]
According to the inventor, this lamp will give a light of 100 carcels
per one horse-power, and with a three horse-power six lamps may be
lighted; but we have made no experiments to ascertain the correctness of
these figures.
As for the cost of the glass rods, that amounts to one franc per
two hundred meters length. They can, then, be considered only as an
insignificant expense in the cost of the carbons. We consequently
believe that it will be possible to employ this system advantageously in
practice.--_Th. du Moncel_.
[Illustration: Fig. 3]
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