icst Steps to (ffifcometrj)* {Continued from page 45,) PROBLEM III. To erect a perpendicular on a given line a b,from a given uoint c in it. A- Set off on eacli side of the point c any twoeqxxal distances c d, c e. From d and e ascentres, and with any radius greater than halfc D, describe two arcs… … From any point d as a centre, and with d cas a radius, describe an indefinite arc e c _f.Through f and d draw the line f d e, then joinE and c, which will be the perpendicularrequired.
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![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-193-112.webp)
