On casting this work in print. Coat the iron plate with white lead in egg, then write in mirror-writing, scratching away that field. This done, cover everything with varnish, that is varnish and lead-tin yellow or minium (red lead). When it is dry, put it to soak, and the field of the letters resting on the white-lead-and-egg is what will lift away together with the minium, which, being brittle, will break and leave the letters attached to the copper. Then clear away the field in your own way and the letters will remain in relief with the field sunken. You may also mix the minium with Greek pitch and apply it hot, as said above, and it will be more brittle. And so the letters may be seen better, tint the plate with the fume of sulphur, which combines with the copper.

n o, m f, g

n o, c

8th and 16th. I have squared n and set it aside; likewise I set o aside, unsquared. Then I subtract the rectilinear triangle m f from the larger rectilinear triangle f g, to have its smaller portion. The part that remains to me is squared and equal to the portion set aside, o - subtracting m f from f g, from which f g a piece equal to n was first taken. In effect g alone equals n m. And if I take o from f g, I also take n from f.

If from two equal surfaces equal parts are removed, the remainder will be equal. I have here 2 equal surfaces, namely n o m f and o f g. I will remove o f from each; I say their remainders are equal, that is n m equals g, so g contains in itself m and n. If I take m from g, there remains a rectilinear part of g equal to the curvilinear n, and thus we have squared the curvilinear n. And if it is found what proportion n has with o, then by squaring n you will have squared o: for if o is 1/3 of n, you make n so [figure with letters: n/o]; n will be 2/3 of o, and o is squared, as you see. Yet another way of squaring the lune n: the whole portion n o is as much as the half portion c o, because they are born of circles double one to another, and 1/16 of the greater is worth as much as one eighth of the lesser. Therefore subtract o from each portion, and there remains c equal to n.