The Architectural magazine . the nearest approach to this thatwe can practically obtain, combining in them the concave andthe vertical surface. Card-board might be moulded in the formof a spherical segment, and transparencies might be painted onclass seirments; but we leave to the curious to estimate their ad-vantages and disadvantages, either by discussion or trial. Wefind this spherical surface forced upon our uninformed judg-ments in the case of the heavenly bodies; which, the quantityand quality of the light not being easily cognizable, being left tobe allotted by us to whatever position w
The Architectural magazine . the nearest approach to this thatwe can practically obtain, combining in them the concave andthe vertical surface. Card-board might be moulded in the formof a spherical segment, and transparencies might be painted onclass seirments; but we leave to the curious to estimate their ad-vantages and disadvantages, either by discussion or trial. Wefind this spherical surface forced upon our uninformed judg-ments in the case of the heavenly bodies; which, the quantityand quality of the light not being easily cognizable, being left tobe allotted by us to whatever position we may, are looked uponby us as equidistant, that is, as points on a spherical surface. Description of the Illustrations which accompani^ the foregoing Article. Fig. 23. ah c d represents the square front of a building, orthe opening of a street; g h^ the middle vertical line; f /, a per- On the Pers j>cctivc Plane. 187 ?tt ,/ / ,•-? / / / *-« / / ,-^ / y ^.^^ / ^ ..- ^? ^ .-? y ^^ -—? ? /.-^ iM^ —? :m. pendicular ray to the plane c h: visual rays are drawn from theprincipal points, the superfluous ones of the cone being rejectedtor the present; i k is made equal to / /?, and ef b d is the tra-pezoidal image; a c ox b d becoming e J\ while g h becomesk k. Now, k h is not proportionally so much reduced from g h ase J\s from a c; for a c \s to e f^ as g i is to k ?, or as g h is tok X. Therefore, if the ratio had been equal, g h would havebeen reduced \.okx; but kx\s less than kij; and/: 3^ is lessthan the hypotenuse k h. The inclination of the plane is lessthan half the visual angle subtended by ^ ^. If / were at w, opposite half the height of g ^, then there isneither reduction nor convergence, and the planes coincide. If i be in 7n orm p {,fig 24.), khis again greaterthan k x; and ob-serve the inclina-tion of the planes,viz. the ansrleg h k, or its equal,h k x^ equals halfthe visual anglesubtended by g i rise above pi or fall below vi (y%. 25.), the ratio 24 y /
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Keywords: ., bookcentury1800, bookdecad, booksubjectarchitecture, bookyear1834
