The system of optical communication proposed by Capt. Gaumet, and
which he names the _Telelogue_, is based upon the visibility of
colored or luminous objects, and upon the possibility of piercing the
opaque curtain formed by the atmosphere between the observer's eye and
a signal, by utilizing the difference in brightness that exists
between such objects and the atmosphere. It is a question, then, of
giving such difference in intensity its maximum of brightness. To do
this, Capt. Gaumet proposes to employ silvered signals upon a black
background. He uses the simple letters of the alphabet, but changes
their value. His apparatus has the form of a large album glued at the
back to a sloping desk. Each silvered letter, glued to a piece of
black cloth, is seen in relief upon the open register. A sort of index
along the side, as in commercial blank-books, permits of quickly
finding any letter at will. Such is the manipulator of the apparatus.
The receiver consists of a spy-glass affixed to the board that carries
the register. For a range of two and a half miles, the complete
apparatus, with a 12×16 inch manipulator and telescope, weighs but
four and a half pounds. For double this range, with a 20×28 inch
manipulator and telescope, the total weight is thirteen pounds. The
larger apparatus, according to the inventor, have a range of seven
miles.
For night work the manipulator is lighted either by one lamp, or by
two lamps with reflector, placed laterally against it.
This apparatus, although well known, and having been publicly
experimented with, has not, to our knowledge, been applied
practically. From a military standpoint, its short range will
evidently not permit it to compete with optical telegraphic apparatus,
properly so called. Perhaps it might rather be of service for private
communications between localities not very far apart, since it costs
but little and is easily operated.