D.

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