374 PERSPECTIVE. 



either of the curves, at the extreme of the other 

 diameter terminated by the curves. 



Abscissa is when any diameter is continued 

 within the curve, terminated by a double ordinate 

 and the curve ; then the part within is called the 

 abscissa. 



Double ordinate is a line drawn through any dia- 

 meter parallel to its conjugate, and terminated by 

 the curve. 



Parameter, or lotus rectum, is a line drawn 

 through the focus, perpendicular to the transverse 

 axis, and terminated by the curve. 



Prob. 34>. To describe an hyperbola by finding 

 points in the curve, having the diameter or axis 

 A B, its abscissa B G, and double ordinate D C. 



Through G draw E F, parallel to C D ; from C 

 and D draw C E aiid D F, parallel to B G, cut- 

 ting E F in E and F. Divide G B and B D, each 

 into any number of equal parts, as four ; through 

 the points of division, 1, 2, 3, draw lines to A. 

 Likewise divide E C and D F into the same num- 

 ber of equal parts, viz. four ; from the divisions 

 on C E and D F, draw lines to G ; a curve being 

 drawn through the intersections at G, a, b, &c. 

 will be the hyperbola required. 



PERSPECTIVE. 



Perspective is the art of drawing upon a plane 

 surface the outlines of objects, so as to give the 

 same representations to the eye that the objects 

 themselves do in nature. 



This art is of the utmost importance in drawing, 

 and its study cannot tae dispensed with by those 



