Worthen, William Ezra, 1819-1897, [from old catalog] ed · New York, Appleton · leaf 21
angle A B C of A B and B 0 ; the angle A B D of A B and 1^ D.The letter at the vertex must always be the central letter. Describe a circle (Fig. 8). Draw the diameter A B. From A and B ascentres, with any opening of the compasses greater than the radius, describetwo arcs cutting each other as at D.… … have equal inclination to each other, and whose lines, if placed one on tjieother, would coincide. By construction, the points 0 and D have, respectively,equal distances from A and B; the line D C can not, therefore, be inclinedmore to one side than to the other, and the angle A 0 D must be equal…
Mechanical drawing
Internet Archive · Library of Congress · Public Domain Mark 1.0. Free to use for anything.
![An illustration from Nicolai Copernici Torinensis De reuolutionibus orbium coelestium, libri VI : Habes in hoc opere iam recens nato, & aedito, studiose lector, motus stellarum, tam fixarum, quàm erraticarum, cum ex ueteribus, tum etiam ex recentibus obseruationibus restitutos: & nouis insuper ac admirabilibus hypothesibus ornatos. Habes etiam tabulas expeditissimas, ex quibus eosdem ad quoduis tempus quàm facillime caculare poteris. Igitur eme, lege, fruere. [Line in Greek] (1543)](https://img.insideoutlibrary.com/img/200/ia-nicolaicopernici00cope-162-91.webp)
