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.

ANNUAL GROWTH

AMOUNT BY WHICH ANNUAL
CUT EXCEEDS

ANNUAL FOREST GROWTH

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

The parts

The circumference of a circle contains 360 degrees.

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,

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

CHARCOAL
15%

SALTPETER
75%

SULPHUR
10%

EXAMPLE 2.

RELATIVE AMOUNTS OF THE VARIOUS CON-
STITUENTS OF BLACK GUNPOWDER

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.

SECOND YEAR
760

FIRST YEAR
698

FOURTH YEAR
292

THIRD YEAR
431

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.

2. Prepare a graph setting forth the following facts:

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.