50 lamps; the most valuable
trials having taken place at the Turin Exhibition. After prolonged
use, a diminution in the fall of potential is produced, to a more
marked degree than in the Edison lamp, and the light can be maintained
constant by increasing the strength of the current in a proportion
that can be determined by means of resistances. The Cruto filament
examined under the microscope appears to be uniformly magnetic, and
is very regular, except at the curved parts where the diameter is
slightly diminished, and it is here that rupture generally takes
place. The great structural regularity of the filament probably
accounts for its high durability, and from the fact that it may
be worked with a higher current than probably any other form of
incandescence lamp. M. Desroziers in a series of experiments obtained
as much as 250 carcel spherical luminous value per horse-power; this
characteristic is one likely to be of great value in electric lighting
by incandescence of high intensity. At present only 20-candle lamps
are made on the Cruto system. The carbon filament, when properly
prepared, is gray in hue and of metallic appearance; it is built up
in very fine laminae indicating the mode of manufacture. The results
obtained with these lamps vary as much as 25 per cent., according to
the care bestowed in producing the filament. If traces of air exist in
the globe, they very quickly manifest themselves by the surface of
the glass becoming blackened, while an increased energy is required to
maintain the brightness of the light.

In the early days of this lamp it was thought necessary to remove
the delicate platinum wire which forms the core of the filament, by
raising the strength of the current sufficiently to destroy it in the
course of manufacture. This, however, was given up, and the platinum
now remains either as a continuous wire or as a series of small
separated granules.

* * * * *

ELECTRIC LIGHT APPARATUS FOR MILITARY PURPOSES.

In the first period of the siege of a stronghold it is of very great
importance for the besieged to embarrass the first progress of the
attack, in order to complete their own armament, and to perform
certain operations which are of absolute necessity for the safety of
the place, but which are only then possible. In order to retard the
completion of the first parallel, and the opening of the fire, it is
necessary to try to discover the location