Voussoir arch of sixteen stones and a forking watercourse
The arch of discrete quantity thrusts obliquely; water striking an angle deepens the banks.
In red chalk the sheet shows a rounded arch built of sixteen joined voussoirs inside a rectangular frame, crowned by a block, with diagonal construction lines and the letters a, b, c, n. The note argues that such an arch of 'discrete quantity' exerts its force along an oblique line, so that the triangle c n b bears no weight. Below, a forking watercourse is drawn, with a note that water striking into the fork's angle deepens the first banks.
On this page
Arch of sixteen stones thrusts obliquely (a c n b)
The voussoir arch is analysed with the letters a c n and b n. The note states that an arch of discrete quantity exerts force along an oblique line, so that the triangle c n b bears no weight.
Forking watercourse deepens the banks
A watercourse is shown splitting into two branches. The note observes that the water striking into the angle of the fork deepens the first banks it meets.