London : Longman, Rees, Orme, Brown, Green, and Longman · leaf 274
ely get thetwisted form ; that is, we make each bed of the courses of stonesa true spiral plane. The principle which I have adopted is, to work the stonesin the form of a spiral quadrilateral solid, wrapped round acylinder, or, in plainer language, the principle of a square-threaded screw: hence it… … 102 should be worked into true spiral planes; but I am not awarethai any rule has yet been published that would enable thestones to be wrought at the quarry into the desired form, or ofany rule by which the true angle at which the courses cross theaxis of the bridge is determined. Fig. 103. is a…
Architecture
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