368; Mr. pE A c ock's Defiriptions of b:firumenis 



T I G. II. (t a B. XIV.) 



As the inftrnment, fig, i. proceeds chiefly by finding the po- 

 fitions of PointSj this is contrived to find the pofitions of Lines, 

 and to determine their limits by their reciprocal interfe6lions. 



ABOCDE is a compound board, to be placed in a vertical 

 pofition. FGHI is the opening, or field of view. KLMN is a 

 loofe board, upon which paper is to be fixed ; and the edges of 

 the faid board are to be rebated, as defcribed in the plan at zz, 

 XYMN and OPQR are grooved receiles, to receive the faid" 

 loofe board, as occafion may require. STUW is a moveable 

 parallelogram, compofed of a rebated flock SU, two like gra- 

 duated rulers ST and UW, and the regulating piece TW ; 

 the whole connected with fcrews, fo as to move freely with a 

 fmall force ; and the diflances between the centers of motion 

 SU or TW to be equal to KF or HQ^. AE and ED are rebated 

 grooves, in which the flock of the parallelogram is to move. 



To life the Injlrument, 



Having fixed the compound board ABOCDE truly vertical, 

 flip the papered board KLMN into the recefs XYMN, or 

 OPQR, as the fubjed to be drawn may render firft neceflary, 

 and Aide the flock SU of the parallelogram into the groove AE, 

 or ED, to correfpond therewith ; then, by moving the fl:ock in 

 the groove with one hand, and at the fame time regulating the 

 parallelogram with the other, the top edge of the ruler UW 

 may be brought to coincide with any line in the original obje^l, 

 and the figured divifions on the edge of the ruler will at the 

 fame time determine the limits thereof, near enough to avoid a 

 confufion of unneceifary lengths of line, &c. The true repre- 

 4 V fentatioii 



