An essay on perspective Willem Jacob Gravesande 551675314
<?xml version="1.0" encoding="UTF-8"?> <div> <h2 xmlns="http://www.w3.org/1999/xhtml"> <span class="headingNumber">212.</span> <span class="italics"> A Demonſtration of the Inclination of the Looking- <br /> Glaſs. </span> </h2> <p xmlns="http://www.w3.org/1999/xhtml"> 48. Let A B be a Ray, proceeding from ſome <br /> Point of an Object. We are to demonſtrate, if the Line D I hath the Inclination given to a <br /> Picture, and the Looking-Glaſs G H hath the In- <br /> clination we have preſcribed, that the Angle <br /> B a F, will be equal to the Angle B C D. Now to <br /> prove this, draw the Line F I parallel to the Ho- <br /> rizon, then the two Angles I D F and D F I, of <br /> the Triangle I D F, are together equal to the <br /> Angle D I E; but the Angle D F I, which is the <br /> Inclination of the Looking-Glaſs, is equal to half the Angle D I E, leſs half the Angle I F a; and conſequently it is leſs than the Angle F D I, <br /> by the Quantity of the whole Angle I F a: Therefore if the Angle I F a be added to the An- <br /> gle D F I, we ſhall have the Angle D F a, equal <br /> to the Angle F D I: Therefore the Angle <br /> Fa B will be likewiſe equal to the Angle BCD. Which was to he demonſtrated. </p> <div xmlns="http://www.w3.org/1999/xhtml" class="floatingText"> <div class="floatingText_body"> <h3> <span class="headingNumber">212.1.</span> </h3> <div class="notemarginLeft" id="note-0196-01">Fig, 75.</div> <div class="notemarginLeft" id="note-0196-02">19.</div> <div class="notemarginLeft" id="note-0196-03">16. 47.</div> <div class="notemarginLeft" id="note-0196-04">19.</div> </div> </div> <p xmlns="http://www.w3.org/1999/xhtml"> In reaſoning nearly after the ſame Manner, <br /> we demonſtrated what is mentioned concer- ning the Inclination of the Mirrour, when the <br /> Box is inclin’d a little backwards. </p> <div xmlns="http://www.w3.org/1999/xhtml" class="floatingText"> <div class="floatingText_body"> <h3> <span class="headingNumber">212.1.</span> </h3> <div class="notemarginLeft" id="note-0196-05">47.</div> </div> </div> <h2 xmlns="http://www.w3.org/1999/xhtml"> <span class="headingNumber">213.</span> <span class="head">FINIS.</span> </h2> <div xmlns="http://www.w3.org/1999/xhtml" class="figure"> <img src="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0196-01" alt="" class="graphic" /> <span class="">0196-01</span> </div> </div>