PERSPECTIVE. 385 



Upon the same principle the row of arches 

 (Fig. 4.) is drawn. The width of the arches and 

 piers is obtained in the same manner as was shown 

 in Fig. 2. ; viz. by laying their dimensions upon the 

 ground-line AB, and drawing lines to the dis- 

 tance-point. The curves of the arches are then 

 found, by drawing the lines which correspond to 

 those in half the square, Fig. 3., in the same man- 

 ner as described above for the circle. 



Fig. 5. shows the appearance of circles drawn upon 

 a cylinder, when H I is the horizontal line. The 

 circle drawn on the cylinder at that place is seen 

 exactly edgeways, and appears only as a straight 

 line; that next above it is seen a little under- 

 neath; the next still more; and so on, as they 

 rise higher, appearing like so many ellipses of the 

 same transverse diameter, but whose conjugate 

 diameters continually increase in length as they 

 rise above the horizontal line. On the contrary, 

 you see the under sides of the circles drawn below 

 the horizontal lines; but they observe the same 

 law, being so many ellipses whose conjugate dia- 

 meters vary in the same proportion. A little re- 

 flection on this simple example will enable those 

 who draw to avoid many ridiculous mistakes which 

 are sometimes committed, such as showing the two 

 ends of a cask, or the top and bottom of a cylinder, 

 at the same time. 



PL 7- Fig. 1. shows the method of drawing a 

 building, or other object, in oblique perspective. 

 A B is the horizontal line, and C D the ground-line 

 parallel to it as before. Here neither of the sides 

 of the house is parallel to the picture, but each 

 goes to its respective vanishing point. Having 

 fixed on the nearest corner E, draw EB, at plea- 

 sure, for one side, and choose any point F for the 



VOL. II. C C 



