166 Improved Geometrical Plotting Quadrant, &e. 



answering to A, then bring the parallel up to the point A 

 answering to the side CA, and by the nut move the per- 

 pendicular till B A answers to the given side B A; next bring 

 down the limb CH to touch B, and on CB may be read 

 the other side, while HG will show the angle C, and IH 

 + 90° the L B, whence all the six parts are known. 



Third. — To set a Triangle having two Sides, and an Angle 

 opposite to one of them given. 

 Let ABC be the triangle, AC and CB the given sides, 

 and A the given angle: first read the angle A on FG, and 

 set the limb CG thereto ; then push up the parallel to the 

 division at A, answering to CA, and with one hand work 

 the nut and with the other move the limb CH, till they 

 touch at B, the division answering to the side CB; then 

 BA is the side sought, and the arc GH will show the L C, 

 andlH + 90° the Z B. 



Fourth.— rib set a Triangle having two Angles, and a Side 

 opposite to one of them given. 

 Let ABC be the triangle, A and C the given angles, and 

 BA the given side : first, set FG to the angle A, and GH 

 to the angle C; then push the perpendicular up or down 

 with one hand, w^hile the other works the nut, till the given 

 side BA, on the parallel, is applied exactly between the 

 limbs CH and CG; then I H + 90° will show the remain- 

 ing angle B ; and on CB and C A may be read the leugths 

 of those sides. 



Fifth. — To set a Triangle whose three Sides are given. 

 Let ABC be the triangle; on the limb CH seek tbe 

 point B, answering to the sideCB; then, using one hand 

 to move the perpendicular, and the other to turn the nut, 

 let an assistant at the same time, with his right hand, gently 

 move the limb CH, while you cause the top corner of the 

 perpendicular always to touch the point B; at the same time 

 let the assistant move the limb CG with his left hand, till 

 the lengths of CA and BA on their respective scales are 

 found to intersect each other, when FG will show the / A, 

 GH the t C, and HI -f 90° the l B. 



My 



