A compleat treatise on perspective, in theory and practice; on the true principles of Dr. Brook Taylor. Made clear, in theory, by various moveable schemes, and diagrams; and reduced to practice ... Containing diagrams, views, and original designs, in architecture, &c. ... All originals; / invented, delineated, and, great part, engraved by the author, Thomas Malton.

  • Malton, Thomas, 1726-1801.
Date:
1778
Catalogue details

Licence: Public Domain Mark

Credit: A compleat treatise on perspective, in theory and practice; on the true principles of Dr. Brook Taylor. Made clear, in theory, by various moveable schemes, and diagrams; and reduced to practice ... Containing diagrams, views, and original designs, in architecture, &c. ... All originals; / invented, delineated, and, great part, engraved by the author, Thomas Malton. Source: Wellcome Collection.

    395/426 (page 287)
    For the Steps; from O, Lines are drawn through the extremes A> B, C, &c. on either Side, till they cut the Floor, or leaves of the Screen, at a, b, c, &c. and from, a, b, &c. to the Vanifhing Point of the Steps, on the Floor, and on the Leaves, being parallel to them. Other wife, they are drawn to that Point in the Vanifhing Line, of each Leaf, in which, the Vanifhing Line of the Plane of Shade of the Step cuts it. Or, drawing through both extremes, of each Sten, as B and D, &c. cuting the Shadows of both Sides, on the fame Plane, the Va- nilhing Point is unneceffary ; but when it falls within bounds, it is the moil corredL In this Cafe (viz. of Lines inclined to the Plane of Proje&ion) the Vanifliing Line of the Plane of Shade is neceffary, when the Shadow is projected on various Planes, but it is not fo eafily determined, as for Shadows projected by the Sun ; nothing more being required than to draw a Right Line through the Vanifhing Points, of the Line and of the Rays, becaufe its diftance is fuppofed infinite; and confe- quently, the fame Vanifhing Line of any Plane of Shade, ferves for all Lines which are parallel. But, here, the Light being at a fhort diftance, it cannot poffibly be in the Vanifhing Line, which is at an infinite diftance ; except apparently fo, when it happens to be lb lituated, in refpectof the £ ye. That VL is the Vanifliing Line of the Plane of Shade of AB, is man.fell; and is determined either by means of the horizontal VanifhingTine (H L) or the vertical Vanishing Line (MM) of the Wall, W, on which the Shadow would be projected, the Screen being out of the way. ' For, AB, cuts the. Wail, being prodcced, at P, as the Floor at A ; and V O reprefents a Line parallel to AB; which, is a Ray of Light in the fame Plane with AB, cuting the Floor, at G, and the Wall, at Q. Confequentl.y, G A, produced, is the Shadow of AB, on the Floor; and, P(^produced, is its Sha¬ dow on the Wall.; the former cuts the Vanifhing Line of theJFIoor, at L, the latter cuts the vert cal Vanifhing Line-at M; both which, are in the fame Right Line palling through V ; and, fince L and M are Vanifhing Points of'the Shadow, VL is, confequently, the Vanifliing -Line of the Plane of /Shade, occafioned by the Line AB (Theorem io.) k |,/ in cs tp;,). v .)!•:» ini 2. The Shadow of the Screen, on the Wall and Cieling, may be thus project d. Through, A, B, &c. at the bottom of the Screen, draw SA, SB, &c. and pro¬ duce them to the Interfedtion of the Wall (W) with the f loor, cuting it at i, 2, &c. from which Points, draw Perpendiculars up the Wall ; and, through the Angles F, G, &c, at the top, draw OF, OG, &c. cuting the Perpendiculars, cor- relponding with AF, &c. at f g, &c. and draw/g, gh, &c. But .the Ray O/, cuts the Cieling.; wherefore, having found f, the Seat of the Light on the Cieling., draw fi, to that Point -where the Perpendicular, from 4, .cuts the InterfedUon of the Wall with the Cieling; and 07, produced, limits the Shadow, at /,; let it be produced, alfo, till it cuts the Perpendicular at k, and join 7 k, cuting the Interfedlioti aty, and join ;/. This procels would be indifpenlibly neceffary, provided the Lines, HI, &c, were not parallel to the Ceiling; but being fo, they are drawn either parallel to the.Line (as for 77/) or to the lame Vanifhing Poiuit (as for IK), A ifghj.ikl, -are the extremes of the Shadow.of the Screen, on the Floor, Wall, and Cieling. By/the lame means, the Shadow of A B, may be projected on the Screen, thus. Draw SA, SB, &c. cuting AF, the Seat of AB on the Floor, at n, o, p, andq; -from which, draw Perpendiculars, cuting AB, at A, B, &c. through which Points, draw OAa, &c. cuting the correfponding angles of the Screen, at a, b, c, &c. which, being joined by Right Lines, give the lame Shadow as before. This procefs, though fhorter, is by no means fo cor re A and mafterly ; hut, as it is performed in lefs room, it maybe applied when the inclination is fuch, that the Vanifhing Points are very remote. 3. The Shadow of the Table, on which the Candle Rands may be thus determined. Having obtained the Seat (s) of the Light on the Table, and (S) on the Floor, through s, draw a b, parallel to the Horizon, alfo c d, and e f at pleafure, cuting the Horizontal Line, at H, and, F; and through S, on the Floor, draw He, and F^, indefinite; alfo ab, parallel to ab. Then, Rays drawn, from O, through the extremes of thofe Lines, viz. Ga, O c, &c. (being produced) will cut the correfponding Lines in the Shadow of each, refpedtively, by which means as many points may be obtained as are neceffary, for .obtaining the.true curv.e of the Shadow, which is a Circle, the Table being circular.