2. What are the contents of a plank 16in. wide and 18ft. 9in. long? Ans. 25 sq. feet. 3. How many feet in a plank 21in. wide and 24ft. long? Ans. 42 sq. feet.

4. How many feet in a plank 17in. wide at one end and 13in. at the other, and 20ft. long? Ans. 25 sq. feet.

See Rule for Trapezoid.

5. What are the contents of a plank 24ft. long, 15in. wide at one end, and tapering to a point at the other?

See Rule for finding area of Triangle.

Ans. 15 sq. feet.

ART. 376. TO FIND THE CONTENTS OF JOISTS, SCANTLING, ETC.

Multiply the breadth in inches by the thickness, and this product by the length in feet; divide the product by 12, and the quotient will be the contents in feet.

Ex. 1. What are the contents of a scantling 6in. wide, 3in. thick and 15ft. long? Ans. 22 sq. feet. 2. What are the superficial contents of a joist 18ft. long, 4in. wide and 3in. thick? Ans. 18 sq. feet. 3. How many feet of lumber in a beam 22ft. long, 8in. wide and 3in. deep? Ans. 44 sq. feet. ART. 377. Practical measurers of lumber employ methods much shorter than those just given. We will illustrate by an example:

Suppose a plank to be 24 feet long, 1 foot wide and 1 inch thick. Its contents are 24 sq. feet.

=

The length remaining the same, suppose it had been 15 inches wide? The contents would evidently be 30 feet, because the width has been increased 3 inches = of a foot, and therefore the contents would also be increased one fourth of what they were. If it had been 16 inches wide, the contents would have been increased one third, and there

fore would have been 32 feet. If the width had been 18 inches, the area would have been increased one half, and would have been 36 feet. Hence, we have this general rule:

When the plank is 1 foot wide and 1 inch thick, the contents will be just as many square feet as there are feet in the length; and for every additional inch in the width we must add to the contents of the number of square feet.

The same principle holds good when the width is less than 1 foot. In such cases we subtract of the contents for each inch less than 1 foot.

If the thickness should be more than 1 inch, we must increase the contents by an additional amount; for example, if the thickness be 1 inches, we must increase the area one fourth of the previous amount; if 1 inches, we must add one half, and so on.

Ex. 1. What are the contents of a board 18ft. long and 16in. wide? Ans. 24 sq. feet. 2. Suppose the plank of the same length, but 20in. wide?

Ans. 30 sq. feet.

3. Suppose it to be 16in. wide and 1 in. thick?

Ans. 30 sq. feet.

4. Suppose it to be 18in. wide and 14in. thick?

Ans. 401 sq. feet.

5. Suppose it to be 10in. wide and lin. thick?

Ans. 15 sq. feet.

6. Suppose it to be 8in. wide and 14in. thick?

Ans. 15 sq. feet.

CONTENTS OF BINS AND CRIBS.

ART. 378. It is sometimes desirable to know how many bushels of corn, wheat or other grain may be contained in a box or bin of given dimensions.

For this purpose we employ the following

RULE.

Measure the length, breadth and depth of the box in inches; multiply these three dimensions together, and divide the product by 2150.42; the result will be the number of bushels.

Ex. 1. How many bushels of wheat can be contained in a box 6ft. 8in. long, 4ft. 2in. wide and 3ft. 6in. deep?

Ans. 78.12+ bushels. 2. How many bushels of corn in a crib 14ft. long, 9ft. 2in. wide and 8ft. 4in. deep? Ans. 859.36+ bushels.

Another very easy method is this:

Multiply together the length, breadth and depth of the crib, taken in feet and decimals of a foot, and then multiply this product by the result will give the contents in bushels, very nearly.

The reason of this Rule is, that a cubic foot is very nearly of a bushel.

Ex. 1. How many bushels of barley could be contained in a box 8ft. long, 5ft. wide and 4ft. 6in. deep?

Ans. 144 bushels. 2. If a bin be 10ft. long, 6ft. 3in. wide and 5ft. 6in. deep, how many bushels of potatoes would it contain?

Ans. 275 bushels.

3. How many bushels of corn could be contained in a crib 16ft. long, 12ft. 6in. wide and 8ft. 3in. deep?

Ans. 1320 bushels.

TEN CENTIMETERS.

ONE DECIMETER.

APPENDIX.

THE METRIC SYSTEM OF WEIGHTS AND MEASURES.

ARTICLE 1. The METRIC SYSTEM of Weights and Measures is based upon the decimal plan of Notation.

ART. 2. It is called METRIC because the METRE* is taken as the standard or unit of measure. The METRE is the one-tenmillionth part of the distance on the earth from the equator to the pole; it is very nearly 39.37 inches, or 3.28 feet, in length.

ART. 3. This system originated in France about the year 1795, and was intended for universal adoption in order to introduce a uniform system of weights and measures in place of the confused and irregular plan then in use.

ART. 4. It has been adopted, wholly or in part, by several of the nations of Europe; in Great Britain and the United States its use is permitted and recommended, though not compulsory.

ART. 5. One of the principal recommendations of the Metric System is the ease with which the TABLES can be learned. When we have fixed upon the unit or standard of measure, all denominations ascend and descend regularly by multiplying or by dividing by 10, and the names of these denominations

*

Metre, from the Greek word Metron, meaning "measure

31*

365

"