4. Falling of a weight.

5. Drying of clothes.

6. Making an iron casting.

7. Decay of vegetables.

8. Sprouting of seeds.

9. Flying an aeroplane.

10. Growth of a plant.

11. Grinding of grain.

12. Sawing a board.

13. Pulverizing stone.

14. Making toast.

15. Sweetening tea or coffee with sugar.

16. Burning wood or gas.

(3) THE METRIC SYSTEM

=10. The Metric System.=--In order to study the three states of matter with sufficient exactness it is necessary to employ a system of measurement. The system universally employed by scientists is called _The Metric System_. In many respects it is the most convenient for all purposes. Every student should therefore become familiar with it and learn to use it. At the present time, not only do scientists everywhere use it, but many countries have adopted it and use it in common measurements. It was legalized in the United States in 1866. The metric system was originated by the French Academy of Sciences during the latter part of the 18th century. There were so many different systems of weights and measures in use, each country having a system of its own, that commerce was much hindered. It was therefore decided to make a system based upon scientific principles. The length of the earth's quadrant pa.s.sing from the equator to the pole was determined by surveying and computation. One-ten-millionth of this distance was selected as the unit of length and called a _meter_. Accurate copies of this meter were made and preserved as standards.

Later surveys have shown that the original determination of the earth's quadrant was not strictly accurate; so that after all the meter is not exactly one-ten-millionth of the earth's quadrant.

=11. The Standard Meter.=--The standard unit of _length_ in the metric system is the _meter_. It is the distance, at the temperature of melting ice, between two transverse parallel lines ruled on a bar of platinum (see Fig. 3), which is kept in the Palace of the Archives in Paris.

Accurate copies of this and other metric standards are also kept at the Bureau of Standards at Washington, D. C. Fig. 4 shows the relation between the inch and the centimeter (one-hundredth of a meter).

=12. Units and Tables in the Metric System.=--The metric unit of _area_ commonly used in physics is the _square centimeter_.

[Ill.u.s.tration: FIG. 3--The standard meter.]

The standard unit of _volume_ or capacity is the _liter_. It is a cube one-tenth of a meter on each edge. It is equal to 1.057 quarts. It corresponds, therefore, to the quart in English measure.

[Ill.u.s.tration: FIG. 4.--Centimeter and inch scales.]

The standard unit of _ma.s.s_ is the _kilogram_. It is the ma.s.s of 1 liter of pure water at the temperature of its greatest density, 4C. or 39.2F.

The three princ.i.p.al units of the metric system, the _meter_, the _liter_, and the _kilogram_, are related to one another in a simple manner, since the liter is a cube one-tenth of a meter in each dimension and the kilogram is the ma.s.s of a liter of water. (See Fig. 5.)

The metric system is a _decimal_ system that is, one unit is related to another unit in the ratio of _ten_ or of some power of ten. This is indicated by the following tables:

_Metric Table of Length_

10 millimeters (mm.) equal 1 centimeter.

10 centimeters (cm.) equal 1 decimeter.

10 decimeters (dm.) equal 1 meter.

10 meters (m.) equal 1 dekameter.

10 dekameters (Dm.) equal 1 hectometer.

10 hectometers (hm.) equal 1 kilometer.

10 kilometers (km.) equal 1 myriameter.

The measures commonly used are the _centimeter_, _meter_ and _kilometer_.

_Metric Table of Ma.s.s_ (_or Weight_)

10 milligrams (mg.) equal 1 centigram.

10 centigrams (cg.) equal 1 decigram.

10 decigrams (dg.) equal 1 gram.

10 grams (g.) equal 1 dekagram.

10 dekagrams (Dg.) equal 1 hectogram.

10 hectograms (hg.) equal 1 kilogram.

10 kilograms (kg.) equal 1 myriagram.

The ma.s.ses commonly used are the _milligram_, _gram_ and _kilogram_.

Notice in these tables the similarity to 10 mills equal 1 cent, 10 cents equal 1 dime, 10 dimes equal 1 dollar, in the table of United States money.

Other tables in the metric system are built upon the same plan. Learn the prefixes in order thus: milli, centi, deci, deka, hecto, kilo, myria. The first three prefixes are Latin numerals and represent divisions of the unit. The last four are Greek numerals and represent multiples. In these tables, milli means 1/1000, centi means 1/100, deci means 1/10, deka means 10, hecto, 100, kilo, 1000, myria, 10,000. Two other prefixes are sometimes used, _micro_ which means 1/1,000,000; as microfarad or microvolt, and _meg_ which means 1,000,000, as megohm meaning 1,000,000 ohms.

=13. Advantages of the Metric System.=--_First_, it is a decimal system; _second_, the same form and prefixes are used in every table; _third_, the standards of length (meter), volume (liter), and ma.s.s (kilogram) bear a simple relation to one another. This simple relation between the three standard units may be given thus: _first_, the liter is a cubic decimeter, and _second_, the kilogram is the ma.s.s of a liter of water.

(See Fig. 5) Since the liter is a cubic decimeter, the length of one side is 10 cm. The liter therefore holds 1000 ccm. (10 10 10).

Therefore, 1 liter = 1 cu. dm. = 1000 ccm. and since 1 liter of water has a ma.s.s of 1 kg. or 1000 g., then 1000 ccm. of water has a ma.s.s of 1000 g., or _1 ccm. of water has a ma.s.s of 1 g._

[Ill.u.s.tration: FIG. 5.--One liter of the water has a ma.s.s of one kilogram.]

The following table of equivalents gives the relation between the most common English and metric units. Those marked (*) should be memorized.

(*) 1 meter = 39.37 inches. 1 cu, in. = 16.387 ccm.

(*) 1 inch = 2.54 cm. 1 cu. ft. = 28315 cm.

1 foot = 30.48 cm. 1 cu. m. = 1.308 cu. yd.

1 mile = 1.609 km. (*) 1 liter = 1.057 qt.

1 sq. in. = 6.45 sq. cm. (*) 1 kg. = 2.204 lbs.

1 sq. cm. = 0.155 sq. in. 1 g. = 15.44 grains.

1 sq. m. = 1.196 sq. yd. 1 lb. = 0.4536 kg.

1 acre = 0.405 ha. 1 oz. = 28.35 g.

1 hectare = 2.45 acres. 1 g. = 0.0353 oz.

THE C. G. S. SYSTEM. Scientists have devised a plan for expressing any measurement in terms of what are called the _three fundamental units of length_, _ma.s.s_, and _time_. The units used are the _centimeter_, the _gram_ and the _second_. Whenever a measurement has been reduced to its equivalent in terms of these units, it is said to be expressed in _C.G.S._ units.