Squaring Curvilinear Figures into Equal Rectilinear Areas
Rows of lunes and circular segments transformed into equal triangles and squares; 'Treatise on continuous quantity'
A very large sheet densely ruled into rows of curvilinear figures — lunes (falcate), circular segments (porzioni) and their combinations — each accompanied by a short note on how it is 'squared' (quadrasi), that is, transformed into an equal rectilinear figure by moving convex parts into concave ones. The header announces the transmutation of equal rectilinear surfaces into various curvilinear figures and the converse, and the foot of the page bears the heading 'Treatise on continuous quantity'. Marginal statements set out the governing principles: equals taken from equals leave equals, and figures in double proportion superimposed leave an excess equal to the smaller. Letter labels a, b, c and others mark the parts to be exchanged in each demonstration.
On this page
Transmuting rectilinear surfaces into curvilinear figures
The programmatic header states the aim of the whole sheet: the transmutation of equal rectilinear surfaces into various curvilinear figures, and likewise the converse — the transformation running in both directions.
Squaring a lune by filling concavity with convexity
A representative demonstration: a is worth b c, and it is squared by filling the concavity of the two lunes with their own convexity — the basic move of cutting a convex piece and setting it into the matching concave gap.
Principle: equals taken from equals leave equals
The upper margin of the left half states the axiom the proofs rely on: if you take equal parts from equal things, the remainders are equal to one another; and if two surfaces in double proportion are entirely superimposed, the excess of the larger is worth the smaller.
Lunes squarable because from double circles
One figure notes that the lunes are squarable in themselves because they are those of the double circles of Zenophon, and the remainder is squarable too — invoking the classical lune-quadrature tradition.
Maxim: what is given back leaves no lack
Beneath a segment divided into n and m (each a quarter of the whole), a terse maxim reads: to whom is given back what was taken, there is no lack — a memorable statement of the conservation of area across the transformations.
Heading: Treatise on continuous quantity
At the centre of the lower margin the sheet is titled 'Treatise on continuous quantity', framing the whole collection of quadrature demonstrations as part of a treatise on continuous magnitude.
