Chapter LXXXIV: Section 98: Apparatus for Drawing Curves

See Gearing, Section 40; Ellipsograph, Section 34.

=1807. Cyclograph,= for describing arcs, the chord and versed sine being given. Fix pins at ~A~ and ~B~, fasten together at ~C~ two slips of wood, hold the pencil at ~D~, and move the slips round, keeping them against the pins. See also No. 11.

=1808. Hyperbolagraph.= Height and focus are given as for 1809, and string fixed to ~B~, and focus ~A~; the arm is pivoted at ~C~, and the pencil used as described for No. 1809.

=1809. Parabolagraph.= The height of parabolic curve ~H~ and focus ~A~ are given. A string is fastened to end of set square at ~B~, reaching to ~C~, and the other end fixed to a pin in the focus ~A~. A pencil held in the loop and kept against edge of set square as it is moved to left or right will describe the parabolic curve.

=1810. Cycloidograph,= describes the hypo- or epi-cycloid. A modification of this is used to draw the curves of the teeth of wheels.

=Pentagraph,= for reducing or enlarging outline drawings, No. 1924.

=Helicograph,= to describe a regular helix by a central fixed bevil
wheel which drives the radial bevil wheel screw and scribing pencil,
No. 1925.

=A simple helicograph,= with radial screw and roller nut, which
travels along the screw as the apparatus is revolved on its centre
pin, No. 1926.