MANOGRAPH
Man"o*graph, n. [Gr. thin, rare + -graph: cf. F. manographe.]
(Engin.)
Definition: An optical device for making an indicator diagram for high-
speed engines. It consists of a light-tight box or camera having at
one end a small convex mirror which reflects a beam of light on to
the ground glass or photographic plate at the other end. The mirror
is pivoted so that it can be moved in one direction by a small
plunger operated by an elastic metal diaphragm which closes a tube
connected with the engine cylinder. It is also moved at right angles
to this direction by a reducing motion, called a reproducer, so as to
copy accurately on a smaller scale the motion of the engine piston.
The resultant of these two movements imparts to the reflected beam of
light a motion similar to that of the pencil of the ordinary
indicator, and this can be traced on the sheet of ground glass, or
photographed.
Source: Webster’s Unabridged Dictionary 1913 Edition