The Collaborative International Dictionary of English v.0.48:

Manograph \Man"o*graph\, n. [Gr. ? thin, rare + -graph: cf. F.
   manographe.] (Engin.)
   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.
   [Webster 1913 Suppl.]