Johnston, Philip Devereux, 1855- · New York, D. Williams Company · leaf 76
amepurpose, and is sometimes so used, but the resulting form of the case is not so well adapted to the purposefor which these blowers—that of moving air—are used.The same objection holds good with reference to the2-centre spiral. The draughtsman, however, findsnumerous applications for all of these… … 71 72 A MANUAL OF MECHANICAL DRAWING. Plate 17. The Involute. Fig. 25.—If a string be wound around a circularblock and a pencil be attached to the free end, the blockbeing held to a plane surface, the pencil will, if heldtaut, and the string unwound, describe a curve calledthe involute of a circle,…
Mechanical drawing
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