BENJ. PIKE S, JR., DESCRIPTIVE CATALOGUE. 



and rule will move in a 

 ^^^^_ direction parallel to them- 

 selves. The wheels are 

 somewhat indented, to pre- 

 vent their sliding on the 

 paper ; small ivory cylin- 

 ders are sometimes affixed 

 to the rollers, as in the 

 figure. The circumferences 

 of these are so adjusted, 

 that they indicate with ex- 

 actness the parts of an inch 

 moved through by the 

 rule. 



In rolling these rules, 

 one hand only must be used, 

 and the fingers should be 

 placed nearly in the mid- 

 dle of the rule, that one 

 end may not have a ten- 

 dency to move faster than 

 the other ; the wheels only 

 should touch the paper 

 when the rule is moving, 

 and the surface of the pa- 

 per smooth and flat. 



Price, 12 in., $5.50. 



The T Square. (Figs. 

 41 and 42, page 39.) 

 This is a very useful article 

 in drawing. A ruler, about 

 two to three feet in length, 

 made of hard wood, or 

 steel, is fixed, as a square, 

 to the middle of a piece 

 of hard wood, about one 

 foot long and two inches 

 w T ide, and on one side a loose piece is fastened by a thumb 

 screw, which passes through both pieces, allowing both to be 

 clamped together at any angle, thus forming a bevel. 



The head of the square, applied close to the edge of a 

 true drawing board, will admit of true lines being drawn as 



