To bring square links to acres.
Of square links cut off five of the figures on the right hand, for decimals, and the rest will be acres; then multiply these decimals by 4, for roods, cutting off five figures as before; and the decimals of these again by 40, for perches, when five figures are again to be struck off.
To find the area of a regular polygon.
Multiply the perimeter (or sum of the sides) of the polygon by the perpendicular drawn from its centre on one of its sides, and take half the product for the area.
Or, multiply the area of one of the triangles by the number of sides of the polygon, and the product will be the area of it.
Example.—Required, the area of a regular hexagon, whose side is 40 feet, and the perpendicular 34·64 feet.
40 × 6 = 240 the perimeter.
240 × 34·64 2 = 4156·8 square feet. Area required.
To find the diameter, and circumference of any circle, the one from the other.
Use either of the following proportions:
| as 7 is to 22 | } | { so is the diameter |
| or as 1 is to 3·1416 | } | { to the circumference. |
| as 22 is to 7 | } | { so is the circumference |
| or, as 3·1416 is to 1 | } | { to the diameter. |