Geometric progression 1 3 9 27 in arcs
Nested red-chalk arches with the powers of three, ending in a rectangle and a cube
The sheet is filled with nested red-chalk arcs carrying the numbers of a geometric progression - 1, 3, 9, 27 - the successive powers of three. A short line of mirror-writing notes something 'doubled', and the number 27 is broken down as 9 and 9 and 9 and as 3 and 3 and 3. Rows of little arches run down to a rectangle and, at the foot, to a cube.
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The progression 1 3 9 27
Grouped arches carry the series 1 3 9 27, the powers of three, with 27 resolved as 9 9 and 3 3 3. The notes track how each term triples the last, a continued geometric proportion.
Arches closing on a rectangle and a cube
Three little arches lead to a rectangle, and a further set of four arches ends in a cube. The figures translate the numerical progression into proportioned plane and solid shapes.