Page:An introduction to linear drawing.djvu/98

 ﻿2. A man wishes to cover the walls of a room with cloth. The length of all the sides added together is 675 inches, 7 tenths, the height is 98,4 the cloth is 32 inches wide ; how long a piece will cover the walls ?

Multiply the length by the height, to find the surface or superficies to be covered. The cloth then must have a length which multiplied by its breadth will give the same superficies, and this is found by dividing the su- perficial contents of the walls by the width of the cloth. Paper hangings may be measured in the sanje way.

Ans. 2077 inches or 57 yards.

If the prism be oblique, its surface is found by taking that of ail the parallelograms which form it.

Problem III. To find the surface of a triangle.

Rule. Multiply the base by the height, and take half of the result.

If you please, you may take half the base or half the height, before you multiply, and then there will be no need of halving the result. A triangle is always the half of a parallelogram of the same base and height.

The pupil, it is to be hoped, need not be told that 12 inches make a foot, and 3 feet or 36 inches an English yard. We advert to this, because we have hitherto only measured by inches, and it may be well to say that when feet or yards, inches and decimals are named together, the yards or feet must be brought into inches. To do this, multiply the feet by 12, and the yards by 36. This however is not necessary, when only feet ox yards are named, and the decimals are parts of them, and not parts of inches.

Thus, 8 feet, 4,8 inches are the same as 100,8 inches.

6 yds. 4,5 inches are equal to. . 220,5 inches.

Example 1. Required the extent of a field of a trian- gular shape, of which one side taken for the base, is 154