Parabolic compass and geometric construction
An instrument for tracing parabolas, with a right-angle and parallel construction and a column of numbers.
The upper half of the sheet is filled by a large drawing of a parabolic compass, an instrument for tracing parabolas, shown as a conic figure crossed by a rigid framework. A short note beside it lays out a construction using points a, b, c and d, requiring right angles and parallel lines. Below are numerous small mechanical and instrument sketches, and a separate group of numbers (100, 1600, 16, 12).
On this page
Right-angle and parallel construction
The note sets out a geometric construction lettered grave - b - (c) - c - a - d. It requires that a b c form a right angle and that b c d likewise be right-angled, while b, d and c are to be held parallel.
Parabolic compass
A large instrument dominates the top of the sheet: a conic (ellipse-like) figure spanned by a jointed rigid framework, the parabolic compass used to draw parabolas mechanically. Its arms and pivots are drawn in ink over a lightly ruled construction.
Column of numbers
A short numerical group is set down separately: 100, 1600, 16 and 12. The figures accompany the geometric and mechanical work but are not tied to a worked calculation in the transcription.