EX.—Find the side of a square equal in area to a rectangle in which _l_ = 31 ft. and _b_ = 5 ft. Set the (R.H.) index of B to 31 on A, and under 5 on B read 12·45 ft. on D. To find various lengths _l_ and breadths _b_ of a rectangle, to give a constant area _a_. Invert the slide and set the index of Ɔ to the given area on D. Then opposite any length _l_ on Ɔ find the corresponding breadth _b_ on D. EX.—Find the corresponding breadths of rectangular sheets, 16, 18, 24, 36, and 60 ft. long, to give a constant area of 72 sq. ft. Set the R.H. index of Ɔ to 72 on D, and opposite 16, 18, 24, 36, and 60 on Ɔ read 4·5, 4, 3, 2, and 1·2 ft., the corresponding breadths on D. To find the contents in cubic feet of a cylinder of diameter _d_ in inches and length _l_ in feet. Find area in feet as before, and multiply by the length. If dimensions are all in inches or feet, set the mark _c_ (= 1·128) on C to diameter on D and over length on B, read cubic contents on A. To find the area of an ellipse. Set 205 on C to 161 on D; bring cursor to length of major axis on C, 1 on C to cursor, and under length of minor axis on C read area on D. EX.—Find the area of an ellipse the major and minor axes of which are 16 in. and 12 in. in length respectively. Set 205 on C to 161 on D; bring cursor to 16 on C, 1 on C to cursor, and under 12 on C read 150·8 in. on D. To find the surface of spheres. Set 3·1416 on B to R.H. or L.H. index of A, and over diameter on D read by the aid of the cursor, the convex surface on B. To find the cubic contents of spheres. Set 1·91 on B to diameter on A, and over diameter on C read cubic contents on A. WEIGHTS OF METALS. To find the weight in lb. per lineal foot of square bars of metal. Set index of B to weight of 12 cubic inches of the metal (_i.e._, one lineal foot, 1 square inch in section) on A, and over the side of the square in inches on C read weight in lb. on A. EX.—Find the weight per foot length of 4½in. square wrought-iron bars. Set middle index of B to 3·33 on A, and over 4½ on C read 67·5 lb. on A. (N.B.—For other metals use the corresponding constant in column (2), below). To find the weight in lb. per lineal foot of round bars. Set R.H. or L.H. index of B to weight of 12 cylindrical inches of the metal on A (column (4), below), and opposite the diameter of the bar in inches on C, read weight in lb. per lineal foot on A. EX.—Find the weight of 1 lineal foot of 2 in. round cast steel. Set L.H. index of B to 2·68 on A, and over 2 on C read 10·7 lb. on A. To find the weight of flat bars in lb. per lineal foot. Set the breadth in inches on C to (1)/(weight of 12 cub. in.) of the metal (column (3), below) on D, and above the thickness on D read weight in lb. per lineal foot on C. EX.—Find the weight per lineal foot of bar steel, 4½in. wide and ⅝in. thick.