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



The Protractor (Fig. 33, page 30) is an instrument used 

 to protract, or lay down an angle containing any number 

 of degrees, or to find how many degrees are contained in 

 any given angle. 



The Semicircular Protractor is divided into one hundred 

 and eighty equal parts or degrees, which are numbered at 

 every tenth degree each way, for the convenience of 

 -reckoning either from the right hand towards the left, or 

 from the left towards the right ; or the more easily to lay 

 down an angle from either end of the line, beginning at 

 each end with 10, 20, etc., and proceeding to 180 degrees. 

 The straight side is the diameter of the semicircle, and the 

 mark or small notch in the middle points out the centre. 

 Price, in brass, 4 inch SOcts. 

 5 " 75cts. 



6 inch, divided to one-half degrees, $1.25. 



7 inch, $1.50. 



Ivory Protractors (Fig. 34, page 31), in the form of a 

 parallelogram, or long square, are usually contained in the 

 best cases of mathematical instruments, and are more exact 

 than the common semicircular ones for angles to forty or 

 fifty degrees ; because at and about each end the divisions 

 being further from the centre are larger ; the side of these 

 protractors to be applied to the paper is flat, on which is 

 marked the lines of the plane scale, and that whereon the 

 degrees are marked is sloped away to the edge, that an 

 angle may be more easily measured, and the divisions set 

 off with greater exactness. Price, $1.50 to $4.00. 



Protractors of Horn are, from their transparency, very 

 convenient in measuring angles, and raising perpendiculars. 

 When they are out of use they should be kept in a book to 

 prevent their warping. Price, 4 inch, 2 Sets. 



' 5 " 50cts. 



6 inch, divided to half degrees, 88cts. 



7 " * " " $1.25. 



The Plane Scale. (Fig. 35, page 33.) The divisions 

 used for measuring straight lines are called scales of equal 

 parts, and are of various lengths, for the convenience of 

 delineating any figure of a larger or smaller size, according 

 to the fancy or purposes of the draughtsman. They are a 

 measure in miniature for laying down upon paper, &c., 



