the line the position of the notch 0. Then place the pencil at the required graduation mark and (after removing the protractor) join the point so marked to 0.

• THE EXTENT TO WHICH THE ANNUAL CUT EXCEEDS

THE ANNUAL FOREST GROWTH IN

THE UNITED STATES

EXAMPLE 1. Show graphically by the sector method the relative amounts of the various constituents of black gunpowder if it is made up of Sulphur.

10 per cent Charcoal .

15 per cent Saltpeter

75 per cent

.

.

The circumference of a circle contains 360 degrees. The parts into which it is to be divided in this case are 10 hundredths of it for sulphur, 15 hundredths of it for charcoal, and 75 hundredths of it for saltpeter. That is,

Sulphur
Charcoal
Saltpeter

.10 x 360°, or 36°
.15 x 360°, or 54°
.75 X 360°, or 270°

If a circle is drawn and these angles laid off, the accompanying figure will result.

CHARCOAL

15%

JAL TPE TEA

75%

SULPHUR

10%

RELATIVE AMOUNTS OF THE VARIOUS CON

STITUENTS OF BLACK GUNPOWDER

EXAMPLE 2. Show in similar manner the relative numbers of students in the four classes of the Los Angeles Polytechnic High School if the numbers are as follows:

It is frequently an aid in making the drawing if the figures to be used are tabulated in some such way as the following:

If the angles in the fourth column are laid off on a circumference of convenient size, the figure will have the following appearance.

FIRST YEAR

698

SECOND YEAA

760

FOURTH YEAR

292

THIAD YEAA

43/

In the construction of a graphic chart, care should be exercised in the selection of the lengths of the units to be used so that the figure or diagram may not be of inconvenient size or shape.

Exercise

1. Observing the precaution just given, prepare a diagram showing the temperatures at which various substances melt.

TEMPERATURES AT WHICH VARIOUS SUBSTANCES MELT

SUBSTANCE

MELTING POINT DEGREES CENTIGRADE

Ice
Sulphur
Tin
Lead
Zinc
Aluminum
Silver

0 114 233 330 433 650 954

SUBSTANCE

MELTING POINT DEGREES CENTIGRADE

.

Gold
Copper
Cast iron
Platinum
Iridium

1063 1100 1200 1775 1950

2. Prepare a graph setting forth the following facts :

ABUNDANCE OF THE ELEMENTS IN NATURE

LIST OF ELEMENTS IN ORDER

OF ABUNDANCE

COMPOSITION OF THE EARTH'S
CRUST INCLUDING THE OCEAN

AND THE ATMOSPHERE

Name
Oxygen
Silicon
Aluminum
Iron .
Calcium
Magnesium
Sodium
Potassium
All others

Per Cent

49.98
25.30
7.26
5.08
3.51
2.50
2.28
2.23
1.86

Frequently the pictorial idea can be effectively used, as illustrated below.

EGG YIELDS. — A record yearly yield (314 eggs) compared with

the yield of an average hen (135 eggs)

The character of the vote at an election can be set forth by such an arrangement as that shown in the accompanying map.

In the diagram setting forth the facts of negro population, observe that the shading of the portion of the circle representing the negro population is itself an aid to the easy interpretation of the diagram.