London : Longman, Rees, Orme, Brown, Green, and Longman · leaf 275
nd the courseforming the key-stone is carried out so as to show that it reallyis the thread of a square-threaded screw wound round a cylin-der, the cylinder being indicated by the two dotted lines. Ifthe threads are cut at right angles to the cylinder, the sectionwould appear as in ^g. lOi; if cut… … In order that these prhiciples may be understood, it is neces-sary to have a clear idea of the nature of a spiral plane ; and,perhaps, the best definition of it is, to consider it as being pro-duced by the twofold motion of the radius of a cylinder; that is,let a radius revolve upon its axis at a…
Architecture
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