draMr line* on the b&ard corresponding to aft, cd; the centre of the curve will be found some-» where on this line. By trial on the copy suppose it is found td be at e; measure from c to e, and from e as centre, with ed as radius, draw the curve, joining the short perpendicular lines from aft. The centre from which the part of the circle in the copy is described can easily be found by adopting any of the methods described in Practical Geometry, as shewn in fig. 25.
Example 24. To draw the circular-headed fire-place in fig. 24. Let aft be the width, bisect it in c, draw cd perpendicular to aft; draw corresponding lines to a by cd on the board; measure from e to a, ft, from these draw lines perpendicular to aft, and equal to fe. From c as a centre, with c/as radius, describe the arch fde. Measure from a and ft to A, h to get the width of jambs, and perpendicular to aft draw hmy measure to m, and draw mn parallel to aft; measure to o, and parallel to cd draw lines oo.
» ' Example 25. To dtaw the Circular-headed window in fig. 25. Let aft be the width, bisect it in c, draw eg perpendicular to aft. From a, ft parallel to eg draw lines to d and e, the termination of the curve. To find the centre from which the curve dfe is described, take the. points e and / in the copy, and from these points, with radius greater than half the distance between them, describe arcs cutting in g, h. From d and 4 in like manner describe arcs cutting in n, m; through nm,gh draw lines meeting in c; c is the centre from which the curve is described. The centre may be found also by trial on the line cd. The sketch may be copied by transferring the various points found, to the paper on the board, proceeding as in the foregoing lessons.
Example 26. To draw part of cellar-plan of house in fig. 26, shewing walls, top of' copperand flue of furnace connected therewith. The sketch without any of the dotted lines is supposed to be given to copy from. By trial in the copy find the centre of the circle, which suppose to be at o; from o draw a perpendicular to ab, parallel to ca, and another line at right angles to this, as oe, touching the line ca in the point e. On the paper on the board draw any two lines intersecting each other at right angles, the point of intersection at o will represent the point o of the copy. Measure from o to d, and from o to e; draw at these points lines at right angles, meeting in the point a. From a measure to b, draw bf parallel to do; in the copy
bisect the side nm of the flue, and draw the line gh at right angles to mn. From h measure to m, n, and from these points draw lines meeting ca in c,s. From o, with proper radius, describe the circle, and from same point with of describe part of a circle, joining / with side of flue mn. Another method of copying this may be adopted. Draw any two lines c a, a b at right angles, meeting in a; from a measure to s, at right angles draw from this point a line and measure sm ; from m parallel to ca draw a line and measure mn; from n parallel to sm draw a line meeting ca in c. The internal flue can be put in by any of the foregoing lessons. From a measure to b, draw b f. Find by trial the centre of the circle, measure the distance of this from the two sides ca, ab, transfer these to the board, and describe the circle as before.
Kniwi 27- To dnnr ¿A* and etUar-fiutt giwem »J^l 27. Indie copj «■rtimie the line d across a, the line ^ across /, across By tzttl find die cailitt of the circlesjoin them by a line pop. Co tk board draw amy line representing one centre-line of the wall /a, and at right angles to it another rfdL From a measure to e and c,c, from thru draw Hues forming one half parallelogram, as in the copy. From a measure tof, and through f draw a line parallel todd; fromf measure to9,4, pot in A, A, and join gji by lines. From a measure to o; draw a line through
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