Worthen, William Ezra, 1819-1897, [from old catalog] ed · New York, Appleton · leaf 38
FlG CONSTRUCTION OF GEOMETRICAL PROBLEMS. 21 terior circle. The chords of the arcs intersected correspond to the sides of thedifferent polygons. The figure gives the polygons such as are usually found in practice, but asimilar figure can be constructed increasing the number of sides as far as maybe… … For the laying out of angles the protractor is used. In its simplest form itconsists of a semicircle of metal or horn of which the edge is divided into 180degrees. To lay off a given angle—say 47° (Fig. 74)—place the edge of the protractor,a b, along the given line and make the centre of the…
Mechanical drawing
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