Plane geometry: triangles, a rhombus, and line segments
Rows of figures keyed to numbered propositions ('ninth of the first')
This leaf sets out a series of small plane-geometry figures in two rows: an equilateral triangle and a rhombus split by its two diagonals in the upper row, and line segments (labelled 10 and 3) with an isosceles triangle whose height is marked in the lower row. A note at the head, 'ninth of the first', cites a numbered proposition in the manner of Euclid's Elements. Several lines of fainter, untranscribed prose run across the lower half of the leaf.
On this page
Proposition reference: 'ninth of the first'
A short note at the top of the leaf reads 'ninth of the first', citing the ninth proposition of a first book in the style of Euclid's Elements. It heads the row of figures below as if illustrating that proposition.
Upper row: equilateral triangle and diagonally-divided rhombus
The first row carries an equilateral (isosceles) triangle marked 1 and a rhombus crossed by its two diagonals marked 2. The diagonals meet at the centre, dividing the rhombus into four right triangles.
Lower row: measured segments and an isosceles triangle
Below stand line segments labelled 10 and 3 and an isosceles triangle whose height is drawn in. The measured segments read as the dimensions to which the triangles are built.