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].