. An encyclopaedia of architecture, historical, theoretical, & practical. New ed., rev., portions rewritten, and with additions by Wyatt Papworth. rmined either by means of visual rays from aIlan, or through the medium of intersections of tlie perspective linesif the upper parts of them on the sofite, which is as much as can berequisite for guiding us to a correct delineation. The same process islo be used for the modilliims on the other sides. The following is an easy method for dividing vanishing lines inperspective. Let AB, CI) be the perspective representation of twopaallels, no in
. An encyclopaedia of architecture, historical, theoretical, & practical. New ed., rev., portions rewritten, and with additions by Wyatt Papworth. rmined either by means of visual rays from aIlan, or through the medium of intersections of tlie perspective linesif the upper parts of them on the sofite, which is as much as can berequisite for guiding us to a correct delineation. The same process islo be used for the modilliims on the other sides. The following is an easy method for dividing vanishing lines inperspective. Let AB, CI) be the perspective representation of twopaallels, no in what plane. It is required to divide the givenportion of /^B on one of them so that its parts shall be the perspectiverepresentation of equal portions of the real line (or in any assignedratio). Draw BE parallel to CD and equal to AB, and divide It into the required number of equal parts or of parts in the desired propor- •« »?>•» lion bepmning at E. Join AE and produce it to meet CD in F. From F draw lines to each of the pointsof division TQIIS of the line AE, and they will cut AB In the required points of subdivision p q r Sect. III. 2458. Sciography, or the doctrine of shadows, is a branch of the .science of projection,ard some preparation has been made for its introduction here in Sect. VI. Cliap. I. ( seq.) on Descriptive Geomelrj, which, if well understood, will remove all difficulty incomprehending the subject of this section. 2459. The reader will understand that in this work, which is strictly architectural, theonly source of light to be considered is the sun, whose rays, owing to his great distance,are apparently parallel and rectilineal. It is moreover to be premised, that such parts olany body as may be immediately opposed to the rays of light arc technically said to be in Chap. IV. SHADOWS. 825
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