30 



BENJ. PIKE S, JR., DESCRIPTIVE CATALOGUE. 



Fi s 33 - any known measure, as 



chains, yards, feet, &c. ; 

 and the plan will be 

 larger or smaller as the 

 scale contains a smaller 

 or greater number of 

 parts in the inch. Hence 

 a variety of scales are 

 useful to lay down lines 

 of any required length, 

 and of a convenient pro- 

 portion with respect to 

 the size of the drawing. 

 If none of the scales 

 happen to suit the pur- 

 pose, recourse should 

 be had to the sector. 



The plane scale (Fig. 

 35),in the common cases 

 of instruments, has the 

 following lines of scales 

 upon it, viz. 1. A line 

 of 6 inches. 2. A line 

 of 50 equal parts. 3. A 

 diagonal scale. 4. A 

 line of chords marked 

 C. 5. Seven particular 

 scales of equal parts, 

 or decimal scales of dif- 

 ferent sizes. The num- 

 bers placed at the beginning of each denote how many of 

 the small divisions at the beginning are contained in one 

 inch, viz. 20, 25, 30, 35, 40, 45, 55. On the lines over the 

 spaces containing the decimal divisions, is marked a line of 

 twelve parts to the same space, answering for measures re- 

 duced from feet and inches. 



The line of chords. This line is used to set off an angle 

 from a given point in any right line, or to measure the quan- 

 tity of an angle already laid down. Thus, to draw an 

 angle of a given number of degrees, say 35, open your 

 compasses to the extent of 60 degrees upon the line of 

 chords, and with that opening of the compasses describe an 

 arch ; then, taking the extent of 35 degrees from the chord 



