Perspective. Page 29. 
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Bed. II. PERSPECTIVE. 29 fhall fuppofe the pidure diredly oppofed to the Fig. eye, and by the help of fuch lines'and points, as we have given, we fhall find the appearance of any objed upon that plane. In what went before concerning the demonftrations, we were obliged to view it fideways; that the eye might fee all the interfec* tions of the feveral lines and planes concerned therein; many of which, in any other pofture, would be hid from the eye; fo that each of thefe figures is really itfelf a piece of perfpedive. But thefe principles being eftablifhed, we fhall have no further occafion for it in that pofition ; but fuppofe it placed diredly before the eye, as it is to be feen from the point of view. In the dired method, we find firft how to place the image of a point in the geometrical plane, in the pidure. Then the image of a line in the geometrical plane is found, by finding the images of the extreme points. Then the image cf any plain figure is found, by finding the reprefentations of all the fides. Thofe of curve lines are found, by finding a good number of points, and drawing a curve regularly thro' them. The image of a line perpendicular to the geometrical plane, is eafily found by having the point or bafe given. And then the image of a floaping line. The image of a folid is had by finding the image of its bafe, and then ereding perpendiculars at the angles, of a proper hight; and joining the tops of them by right lines. In general, the images of all lines in the geometrical plane, which are perp. to the ground line, converge to the point of fight. And thofe that cut it obliquely tend to their accidental point. And the images of all lines parallel to one another, except fuch as are parallel to the pidure, converge to fome point or other. All
Title  Elements of optics. 
Alternative Title  The elements of optics... / W. Emerson.;Perspective: or, The art of drawing the representations of all objects upon a plane. 
Reference Title  Emerson, William, 1768. Elements of optics. 
Creator  Emerson, William, 17011782. 
Subject 
Optics  Early works to 1800. Perspective. 
Publisher  London, J. Nourse. 
DateOriginal  1768 
Format  JP2 
Extent  21 cm. 
Identifier  col147 
Call Number  QC353.E5 1768 
Language  English 
Collection  Color and Optics 
Data contributor  Linda Hall Library, LHL Digital Collections. 
Title  Perspective. Page 29. 
Format  tiff 
Identifier  col147327 
Rights  http://www.lindahall.org/imagerepro/terms/ 
Type  image 
OCR Transcript  Bed. II. PERSPECTIVE. 29 fhall fuppofe the pidure diredly oppofed to the Fig. eye, and by the help of fuch lines'and points, as we have given, we fhall find the appearance of any objed upon that plane. In what went before concerning the demonftrations, we were obliged to view it fideways; that the eye might fee all the interfec* tions of the feveral lines and planes concerned therein; many of which, in any other pofture, would be hid from the eye; fo that each of thefe figures is really itfelf a piece of perfpedive. But thefe principles being eftablifhed, we fhall have no further occafion for it in that pofition ; but fuppofe it placed diredly before the eye, as it is to be feen from the point of view. In the dired method, we find firft how to place the image of a point in the geometrical plane, in the pidure. Then the image of a line in the geometrical plane is found, by finding the images of the extreme points. Then the image cf any plain figure is found, by finding the reprefentations of all the fides. Thofe of curve lines are found, by finding a good number of points, and drawing a curve regularly thro' them. The image of a line perpendicular to the geometrical plane, is eafily found by having the point or bafe given. And then the image of a floaping line. The image of a folid is had by finding the image of its bafe, and then ereding perpendiculars at the angles, of a proper hight; and joining the tops of them by right lines. In general, the images of all lines in the geometrical plane, which are perp. to the ground line, converge to the point of fight. And thofe that cut it obliquely tend to their accidental point. And the images of all lines parallel to one another, except fuch as are parallel to the pidure, converge to fome point or other. All 



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