An essay on perspective Willem Jacob Gravesande 551675314
<?xml version="1.0" encoding="UTF-8"?> <div> <p xmlns="http://www.w3.org/1999/xhtml" id="false"> An ESSAY until C D be equal to twice the Length of the <br /> given Perpendicular. This being done, move <br /> the Needle along the Horizontal Line, ſuppoſe <br /> to R, until the Point of the Thread R S paſſes <br /> through the Point T; then keeping the Thread <br /> tight in this Manner, if the Ruler M N be <br /> mov’d, till its Edge alſo paſſes through the <br /> Point T, and P is the Point wherein the Edge of <br /> the ſaid Ruler croſſes the Part of the Thread <br /> R D, the Line T P will be the Repreſentation <br /> ſought. </p> <p xmlns="http://www.w3.org/1999/xhtml"> The Demonſtration of this is evident from <br /> what is ſaid in n. 59. </p> <h2 xmlns="http://www.w3.org/1999/xhtml"> <span class="headingNumber">178.</span> <span class="head"> <span class="caps" style="font-size: 75%">Method</span> II. </span> </h2> <p xmlns="http://www.w3.org/1999/xhtml" class="italics"> 112. When all the Perpendiculars have the ſame <br /> Length. </p> <p xmlns="http://www.w3.org/1999/xhtml"> Let F G be parallel to the Baſe Line, and F O <br /> equal to the Height of the Eye; aſſume F f, e- <br /> qual to the Length of either of the given Per- <br /> pendiculars, and faſten the Thread fixed in F, in <br /> the Point f. Then raiſe R S perpendicular to <br /> the Baſe Line, which make equal to F f, and <br /> draw S Q parallel to the Baſe Line. This being <br /> done, tranſpoſe the Figures in the Geometri- cal Plane, in ſuch Manner, that the Point R co- <br /> incides with S, and R H with S Q. Then if S Q <br /> be taken for a Baſe Line, and the Appearances <br /> of the Feet of the Perpendiculars be found, the Repreſentations of their Extremities will be <br /> had. </p> <div xmlns="http://www.w3.org/1999/xhtml" class="floatingText"> <div class="floatingText_body"> <h3> <span class="headingNumber">178.1.</span> </h3> <div class="notemarginLeft" id="note-0158-01">Fig. 60.</div> <div class="notemarginLeft" id="note-0158-02">60.</div> <div class="notemarginLeft" id="note-0158-03">109.</div> </div> </div> <h2 xmlns="http://www.w3.org/1999/xhtml"> <span class="headingNumber">179.</span> <span class="head"> <span class="caps" style="font-size: 75%">Method</span> III. </span> </h2> <p xmlns="http://www.w3.org/1999/xhtml" class="italics">113. For Perpendiculars of the ſame Length.</p> <p xmlns="http://www.w3.org/1999/xhtml"> The Figures in the Geometrical Plane being <br /> tranſpoſed in the Manner aforeſaid , aſſume T t, </p> </div>