Elements of plane and solid free-hand geometrical drawing, with lettering; and some elements of geometrical ornamental design, including the principals of harmonic angular ratios, etcIn three parts ..for draughtsmen and artisans; and teachers and students of industrial and mechanical drawing . CIKCLES AND THEIE DIVISIONS. 21 In both of these constructions, use fewer and fewer guides,and at last sketch a circle with no guiding point but its practice often in rapidly drawing circles bj hand on theblack board. The distance from the centre to the circumference of a circle,is called its
Elements of plane and solid free-hand geometrical drawing, with lettering; and some elements of geometrical ornamental design, including the principals of harmonic angular ratios, etcIn three parts ..for draughtsmen and artisans; and teachers and students of industrial and mechanical drawing . CIKCLES AND THEIE DIVISIONS. 21 In both of these constructions, use fewer and fewer guides,and at last sketch a circle with no guiding point but its practice often in rapidly drawing circles bj hand on theblack board. The distance from the centre to the circumference of a circle,is called its radius. The distance across the circle, through itscentre is its diameter. Parallel circles have the same centre, and are called con-centric. A portion of the circumference of a circle, is calledan arc. Ex. 58. Draw circular arcs in various positions, and of variousradii, and length, thus : Ex. 59. Draw parallel arcs and circles, of various radii, andthe former also of various lengths and in various positions,thus ; and then marh their 22 FEEE-HAND GEOMETEICAL DRAWING. Division of Circles. Circles, or arcs, may, like straight lines, have given distancesmarked off upon them, and may be divided into equal parts. The line which joins the extremities of an arc, is called thechord of that arc. When the arc is very short, its length cannotbe ordinarily distinguished from that of its chord. It is onthis principle that any given straight distance may be trans-ferred to a circle or to any curve. Ex. 60. To lay off a given distance on a circle or arc, dividethat distance into a sufficient number of small equal parts, andthen mark off on the circle, or arc, the same number of similarequal parts, thus, where the straight line is the given distance. ? t t ? Ex. 61. Any diameter of a circle divides it into two equalparts, therefore draw several circles, and one diameter in each;but in different positions in the different circles, which may alsobe of various sizes. Ex. 62. Two diam
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmechanicaldrawing
