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Practical perspective

Practical perspective

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1785 Excerpt: ... vaults, The prefent femi-circle I fhall only divide into four, and that by circumfcribing it with a parallelogram, or long fquare, and drawing two diagonals interfering each other in I, and the femi-circle in K K, and lav ing a ruler over C I, bifecting the arch in F; laftly draw the line K K, cutting the parallelogram in L, which line L K is to be transferred to Fig. III. to put it in perfpctftive. Firft then draw a line from the angle E to the point of fight M, fet off the mcafuresofthe diameter of the arch DFon the bafeline, as EN, N O, and from the point N draw a line to the point of diftancc P; which cutting the ray E M in the point Q, E Q will be the width of the front arch D E in perfpective. Then drawing a line from O to the point P, where it cuts the ray E M, in the point R, will be the width of the fecond arch. As there is no more room on the bafe line to take the third arch, a line muft be drawn from N to the point of light M; and through the point R a parallel to the bafc lines R S. Now as R S is under the fame angle with E N, it is the fame breadth in its proper diminution, as has been already proved in the beginning of the book; therefore drawing a line from S to the point of diftance P, it will cut the ray E M in the point T, which gives the third arch. Proceed then to raife perpendiculars V V, &c. from the three points QR T, which interfering the ray H M, will give the higheft of the arches; then from the ray B M, which gives the bottom of the femi-circle, draw diagonals B V, H X, which interfering each other, give the place of the perpendicular Y F, that divides the arch into two; and drawing the ray L M, it will cut the diagonals in two, and the arch in four; laftly, connecting the points BZ, F Z X, with curve lines, you will have the...