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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.

Fig. 4.—Centimeter and inch scales.

The standard unit of mass is the kilogram. It is the mass of 1 liter of pure water at the temperature of its greatest density, 4°C. or 39.2°F.

The three principal 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 mass 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 Mass (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 masses 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 mass (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 mass 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 mass of 1 kg. or 1000 g., then 1000 ccm. of water has a mass of 1000 g., or 1 ccm. of water has a mass of 1 g.

Fig. 5.—One liter of the water has a mass 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, mass, 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.