Worthen, William Ezra, 1819-1897, [from old catalog] ed · New York, Appleton · leaf 39
Fig. 22 CONSTRUCTION OF GEOMETRICAL PROBLEMS. … Use of Tkiangle and Square. Right-angled triangles constructed of wood, hard rubber, celluloid, or metalare very useful in connection with a straight-edge, or ruler, in drawing linesparallel or perpendicular to other lines. To draw lines parallel to each other, place any edge of the triangle in…
Mechanical drawing
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