36 BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



thereon ; these are very convenient, as any proportion may 

 be marked off, from the edge, directly on the drawing, 

 without the use of a pair of dividers ; the scales on the 

 other part are usually f , |, f , f-, and on the other side of 

 the scale 1, 1, If, 2, 2, 2|, 3 inch. 



Price, 6 in. "in ivory, $2.50~ ; 9 in. $3.00.; 12 in. $4.00. 

 " in brass, from - - $1.00. to $3.00. 



The Parallel Rule (Fig. 38, page 37) is used for drawing 

 one or more lines parallel to, or equally distant from, any 

 line proposed. It consists of two straight rules, which are 

 connected together, and always maintained in a parallel 

 position by the two equal and parallel bars, which move 

 very freely on the centre, or rivets, by which they are 

 fastened to the straight rules. 



Price, in black ebony, 6 in., 62c. ; 9 in., 88c. ; 12 in., $1 ; 

 15 in., $1.25; 18 in., $1.50: 

 24 in., $2.50 ; 36 in., $5.00. 

 " in ivory, 6 in., $1.50 ; 12 in., $3.00. 



Double Parallel Rule. (Fig. 39, page 38.) This instru- 

 ment consists of two equal flat rules, and a middle piece ; 

 they are connected together by four brass bars. The ends 

 of two bars are riveted on the middle line of one of the 

 straight rules ; the ends of the other t\vo bars are riveted 

 on the middle line of the other straight rule ; the other 

 ends of the brass bars are taken two and two, and riveted 

 on the middle piece, as is evident from the figure ; the brass 

 bars move freely on their rivets, as so many centres. The 

 advantage of this rule is, that in using it the movable rule 

 may always be so placed, that its ends may be exactly over, 

 or even with, the ends of the fixed rule ; whereas, in the 

 former kind, they are always shifting away from the ends 

 of the fixed rule. Price, 6 inch, ivory, $3.50. 



" 12 " "" $7.00. 



EcTchardCs, or Rolling Parallel Rule. (Fig. 40, page 

 38.) This is a rule of black ebony, with slips of ivory laid 

 on the edges of the rule, and divided into inches and tenths. 

 The rule is supported by two small wheels, which are con- 

 nected together by a long axis, the wheels being exactly of 

 the same size, and their rolling surfaces being parallel to the 

 axis ; when they are rolled backwards or forwards, the axis 



