42^ GEOMETR"£. 



Of the preceding three forms of scales for two figure^ 

 the first is a decimal scale, for taking off common num- 

 bers consisting of two figures. The other two are duo-» 

 decimal scales^ and serve fqr feet and inches. 



In order to construct the other lines, 4cscrtbe a 'circum- 

 ference with any convenient radius, and draw the diame- 

 ters A B, D E, at right angles to each other ; continue 

 B A at pleasure toward F 5 through D draw D G parallel 

 toBFj and draw the chords BD, BE, AD, AE. Cir- 

 cumscrihe the circle with the square HMN, whose side^ 

 HM, MN, shall be parallel to AB, ED, 



2, To cctistri^'ct the Line of Chords* 



Divide the arc AD into 90 equal parts ; mark the iotl\ 

 divisions with the figures 10, 20, 30, 40, 50, 60, 70, 80, 

 po ; on D, as a centre, with the compasses, transfer the 

 several divisions of the quadrantal arc, to the chord AD, 

 which marked with the figures corresponding, will bq 

 31 line of phord?. 



Note. In the construction of this and the fallowing 

 scales, only the primary divisions are drawn ; the inter* 

 mediate ones are omitted, th^^t the figure may not appeav 

 too much crowded. 



3. To construct the L'lns of ' Rhumbs^ 



Divide the arc BE into 8 equal parts, which mark 

 ^vith the figures i, 2, 3, 4, 5, 6, 7, 8 ; and divide each of 



those 



