[Illustration: FIGS. 21 AND 22.--FRONT VIEW AND LONGITUDINAL SECTION
OF THE MANGIN PROJECTOR.
(Scale 1/15). A. Elliptical mirror. B. Arm of the same. C. Nut for
fixing the mirror. D. Support of the mirror. E. Occultator. F. Support
for same. G. Lever for maneuvering the occultator. I. Support of the
occultator rod. J. Screw for fixing the mirror support. K. Screw for
fixing the support of the occultator rod. L. Screw for fixing the
occultator support.]
The apparatus shown in Figs. 21 and 22 permits of signaling in three
ways:
1. _Upon the Clouds._--In this case the mirror, A, is removed, and the
projector inclined above the horizon in such a way as to illuminate
the clouds to as great a distance as possible. A maneuver of the
occultator, E, between the lamp and the mirror arrests the luminous
rays of the source, or allows them to pass, and thus produces upon the
clouds the dots and dashes of the conventional alphabet.
2. _Isolated Communication by Luminous Fascicles._--When it is desired
to correspond to a short distance of 2 or 3 miles, and establish a
communication between two isolated posts, the mirror, A, is put in
place upon its support, B. The luminous fascicle emanating from the
source reflected by the mirror is thrown vertically. By revolving the
mirror 90° around its horizontal axis the fascicle becomes horizontal,
and may thus be thrown in a given direction at unequal intervals and
during irregular times, and furnish conventional signs.
3. _Night Communication upon the Entire Horizon._--When we wish to
correspond at a short distance, say two miles, and make signals
visible from the entire horizon, the mirror, A, is put in place, so
that it shall reflect the luminous fascicle vertically. The fascicle,
at a distance of about fifty feet, meets a white balloon which it
renders visible from every point in the horizon. The maneuver of the
occultator brings the balloon out of darkness or plunges it thereinto
again, and thus produces the signs necessary for aerial communication.
[Illustration: FIG. 24.]
These ingenious arrangements, which depend upon the state of the
atmosphere, do not appear to have been imitated outside of the navy.