Mechanical exercises, or, The elements and practice of carpentry, joinery, bricklaying, masonry, slating, plastering, painting, smithing, and turning . e-scribing Elliptic Arches. The operation of describing an ellipse with astring, though true in principle, is useless inpractice, as the string stretches in such a degreeas not to be depended on, and the degree of ten-sion is in proportion to the length of the string,which is therefore unfit to be used for describingthe curve of an arch of large extent. The tram-mel or elliptic compass is a very accurate instru-ment, butitcan onlybeused forwork
Mechanical exercises, or, The elements and practice of carpentry, joinery, bricklaying, masonry, slating, plastering, painting, smithing, and turning . e-scribing Elliptic Arches. The operation of describing an ellipse with astring, though true in principle, is useless inpractice, as the string stretches in such a degreeas not to be depended on, and the degree of ten-sion is in proportion to the length of the string,which is therefore unfit to be used for describingthe curve of an arch of large extent. The tram-mel or elliptic compass is a very accurate instru-ment, butitcan onlybeused forworksuponasmallscale: this method of description will be foundin Problem V, Geometry. The description of anellipse with a beam compass may be put in exe-cution in arches of any exfent as has been fullyverified in the practice of that distinguishedFrench Engineer, M. Perronet. But the com-mon method with three centres only is extremelylame, owing to the sudden variation of curva-ture, which takes place at the junction of twovery different radii. Prob. I. ^rL€Z,J€>^?^^ ^>-^. >?^ EX Jt/L %? x: ^__^. TUlJTTy^ t!Wnr///\ f ; /\ Wi^^ A c.
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Keywords: ., bookcentury1800, books, booksubjectcarpentry, booksubjectgeometry
