Area of a circle = square of rad. × 3·14159.
Area of an ellipse = product of axes × 0·7854.
Circumference of a circle = diameter × 3·14159.
Solidity of a cylinder = height × area of base.
Area of a circular ring = sum of diameters × difference of diameters × 0·7854.
For the area of a sector of a circle the rule is:—As 360 : number of degrees in the angle of the sector :: area of the sector : area of circle.
To find the area of a segment less than a semicircle:—Find the area of the sector which has the same arc, and subtract the area of the triangle formed by the radii and the chord.
The areas of corresponding figures are as the squares of corresponding lengths.
§ 4.
| 1 mile | = | 1·609 kilometres. |
| 1 kilometre | = | 1093 yards. |
| 1 oz. | = | 28·35 grammes. |
| 1 lb. | = | 453·59 " |
| 1 lb. | = | 0·453 kilogrammes. |
| 28 lb. | = | 12·7 " |
| 112 lb. | = | 50·8 " |
| 2240 lb. | = | 1016 " |
| 1 kilogram | = | 2·2046 lb. |
| 1 gram | = | 0·0022 lb. |
| 1 sq. in. | = | 645 sq. millimetres. |
| 1 sq. ft. | = | 0·0929 sq. metres. |
| 1 sq. yard | = | 0·836 " |
| 1 sq. metre | = | 10·764 sq. ft. |