MATHEMATICAL INSTRUMENTS. 13 



Drawing pencil, 



x Ivory sector, 



11 Ivory parallel rule, 



12 Ivory protractor and plane scale combined. 



The most extensive sets contain, in addition 



13 Pair of proportional compasses, 



14 Pair of triangular compasses, 



15 Pair of bisecting compasses, 



16 Pair of fine steel bow dividers, 



17 Fine steel bow pen, 



18 Fine steel bow pencil, 



19 Small fine drawing pen, 



20 Double drawing pen, 



21 Fine dotting instrument with set of movable rollers, 



22 Needle holder. 



Price, mounted in German silver, $20.00. 

 " larger sets, $35.00 to $80.00. 

 " plain brass sets, $3.25 ; 

 $3.75; 

 $4.50; 



" " " $5.00; 



" " " $9.00. 



