Jor drawing In PerfpeSihe. 371 



the correfponding {ide of the board on your defk or table, and 

 draw the line of its precife length and pofition. 



N. B. If this is thought too operofe, the brafs groove and 

 Aiding pieces M, N, may be rejedled, and the blade of the 

 fquare may be graduated on one or both of its edges at pleafure ; 

 and all lines in the fame diredion may be drawn thereby exa6tly 

 as to their pofitions, and nearly, though fomewhat exceeding, 

 their lengths * ; and their precife lengths may be determined at 

 the fame time the lines in the contrary pofitions are drawn, 

 whofe lengths will be given at the fame time by the lines firft 

 drawn. 



Ht 



This will be efFe«5led, by noticing the numbers upon the blade, and taking 

 thofe next beyond the apparent limits of the line j and by this means the drawing 

 will advance without theleaft confufion. 



'wmm. 



