Met′ric Sys′tem.
The system adopted by the
French convention in 1795, in which all measures of length, area, capacity, and weight are based upon the length of a quadrant of the meridian measured between the equator and the pole.
The origin of the system is due to the government of Louis XV., who named a commission to investigate the best means of reforming the great diversity of weight and measures then used in the different cities and provinces of
France.
These investigations were continued under his successor, and in 1790
Talleyrand distributed among the members of the National Assembly a proposal for the establishment of a single and universal standard of measurement.
A committee from the Academy of Sciences, Borda,
Lagrange,
Laplace, and Condorcet, all men of the highest scientific eminence, were appointed under a decree of the Assembly to report upon the selection of a natural standard.
They proposed, in their report, that one ten-millionth part of a quarter circumference of the globe at the meridian of
Paris should be taken as the unit of lineal measure.
This is undoubtedly a more definite standard than that of the
English and
American systems, which are based upon the length of a pendulum beating seconds in the latitudes of
London and New York respectively.
It may be remarked that the
English and
American determinations of the foot and yard from these sources differ slightly, though not enough to affect any practical result.
The values of the meter are, in English inches, 39.37079; in American inches, 39.368.
The values of the metric measures in the following tables are compared with those of the
English yard.
Van Swinden was one of the commissioners for settling the basis of the system, and gives a lengthy description, from which we derive the following: —
The standard is founded upon the basis of the quadrant of the earth, being the part of the terrestrial meridian contained between the equator and the north pole.
The 10,000,000th part of this quadrantal are was adopted to be the linear measuring unit, which they called “metre,” applying it equally to superficial and solid measures, taking for the unit of the former the square of the decuple, and for that of the latter the cube of the tenth part of the meter.
They chose also for the measuring unit of weight, the quantity of distilled water equal in bulk to the same cube at a certain temperature.
They also decided that the multiples and sub-multiples of each kind of measure, whether of weight, capacity, surface, or length, shall be always taken in the decimal or decuple proportion, as the most simple, natural, and easy for calculation, according to the system of numeration which all Europe has used for many centuries.
The Institute (National Institute of France) ordered a new and actual measure of the whole are of the meridian extending the whole length of France, from Dunkirk on the north to Barcelona in Spain, and passing Paris, an extent of almost 10°. The measurement of this are employed Mechain and Delambre for several years.
They employed rods of platinum of 12 feet in length for measuring the bases; and whole circles, accurately made, for taking the angles to 10ths of seconds, by repeating the measures in different parts of the circumference, and taking the mediums of the whole.
The precision with which the angles were observed is such that, out of 90 triangles which connect the extremities of the meridional are, there are 36 in which the sum of the 3 angles differs from its proper quantity by less than 1 second; that is, in which the error of the three angles taken together is less than 1 second; there are 27 triangles in which this error is less than 2 seconds; in 18 others it does not amount to 3 seconds; 4 are under 4 seconds; and the remaining 3 are under 5 seconds.
Every care was taken to support and dispose the platinum rods properly in measuring the bases.
The extremities of the rods were never brought into contact; an interval being left, which was measured by a tongue of platinum, sliding from the end of one of the rules and carrying a vernier and microscope.
The corrections or allowances for differences of temperature, for obliquities of the line actually measured, and for the elevation above the level of the sea, were also attended to and allowed for. One rod was kept unemployed for a module or standard at 10° Reaumur or 54° Fah.
In deducing the length of the quadrant of the meridian, the are measured by Bouguer and La Condamine in
Peru, in 1736, was taken as an element.
More recent and extended measurements at different points of the earth's surface indicate that the data upon which the metric determinations were founded were inadequate for ascertaining the exact variations in curvature of this irregular ellipsoid at different latitudes, and that consequently the meter is not exactly what it should be, but 10,000,000 meters fall short, according to
Sir J. F. W. Herschel, by 4,008, feet of measuring a meridional quadrant.
This error, amounting to but 1/208 of an inch to the meter, is disregarded.
As before observed, the meter is the basis of all measurements.
From it are derived the following units:—
Of area; the
are, — 1 square decameter.
Of capacity; the
liter, — 1 cubic decimeter.
Of weight; the
gram, — 1 cubic decimeter of water.
The names of the graduations below the unit are formed from the
Latin, and above the unit are formed from the Greek, as follows, the unit being 1: —
| Myria | 10,000 |
| Kilo | 1,000 |
| Hecto | 100 |
| Deka | 10 |
| 1 |
| Deci | 0.1 |
| Centi | 0.01 |
| Milli | 0.001 |
In each of the four classes, — length, area, capacity, and weight, — these prefixes indicate the character of the measure.
Greek for multiples, Latin for fractions.
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Measures of Length.
| Millimetre (.001 metre), | 0.03937 inches. |
| Centimetre (.01 metre), | 0.39371 inches. |
| Decimetre (.1 metre), | 3.93708 inches. |
| Metre (unit), | 39.3708 inches or 3.2809 feet. |
| Dekametre (10 metres), | 32.809 feet, or 10.9363 yards. |
| Hectometre (100 metres), | 328.09 feet, 109.3533 yards. |
| Kilometre (1,000 metres), | 1,093.63 yards, or 0.62138 miles. |
| Myriametre (10,000 metres), | 10,936.33 yards, 6.21382 miles. |
Table.
| 10 millimeters make | 1 centimeter. |
| 10 centimeters make | 1 decimeter. |
| 10 decimeters make | 1 meter. |
| 10 meters make | 1 decameter. |
| 10 decimeters make | 1 hectometer. |
| 10 hectometers make | 1 kilometer. |
| 10 kilometers make | 1 myriameter. |
Measures of Capacity.
The unit for the measure of volumes is a cube whose edge is 1/10 of the meter; that is, a cube whose edge is 3.937 inches. It is called a liter, and is 1/1000 part of a cubic meter.
| Metric Denominations. | English Equivalents. | United States Liquid Measure. |
| Milliliter | 0.001 of a liter | 1 cubic centimeter | 0.00704 gills | 0.061027 cubic inches | 0.27 fluid drams. |
| Centiliter | 0.01 of a liter | 10 cubic centimeters | 0.0704 gills | 0.616271 cubic inches | 0.338 fluid oz. |
| Deciliter | 0.1 of a liter | 1 cubic decimeter | 0.704 gills | 6.102705 cubic inches | 0.845 gill. |
| Liter | 1 liter | 1 cubic decimeter | 1.761 pts. | 61.027052 cubic inches | 1.0567 quart. |
| Decaliter | 10 liters | 10 cubic decimeters | 2.201 galls. | 610.270515 cubic inches | 2.6417 galls. |
| Hectoliter | 100 liters | 1 cubic meter | 2.751 bus. | 6,102.705152 cubic inches | 26 417 galls. |
| Kilditer or stere | 1,000 liters | 1 cubic meter | 27.512 bus. | 61,027.051519 cubic inches | 264 17 galls. |
Table.
| 10 milliliters make | 1 centiliter. |
| 10 centiliters make | 1 deciliter. |
| 10 deciliters make | 1 liter. |
| 10 liters make | 1 decaliter. |
| 10 decaliters make | 1 hectoliter. |
| 10 hectoliters make | 1 kiloliter or stere. |
Weights.
The unit of weight is equal to 1/100000 part of the weight of a cubic meter of pure rain-water weighed in a vacuum.
It is called a gram, and is equal to 15.432 grains
Troy = .0352746 ounces avoirdupois, nearly.
| metric denominations and values. |
| Names. | Number of Grams. | Weight of what quantity of water at maximum density. | Equivalents in denominations in use. |
| | | Avoir'pois. |
| Milligram | 0.001 | 1 cubic millimeter | 0.0154 gr. |
| Centigram | 0.01 | 10 cub. millimeters | 0.1543 gr. |
| Decigram | 0.1 | 1 cub. centimeter | 1.5432 gr. |
| Gram | 1 | 1 cub. centimeter | 15.432 gr. |
| Dekagram | 10 | 10 cub. centimeters | 0.3527 oz. |
| Hectogram | 100 | 1 deciliter | 3.5274 oz. |
| Kilogram or kilo | 1,000 | 1 liter | 2.2046 lbs. |
| Myriagram | 10,000 | 10 liters | 22.046 lbs. |
| Quintal | 100,000 | 1 hectoliter | 220.46 lbs. |
| Millier or ton | 1,000,000 | 1 cubic meter | 2,204.6 lbs. |
Table.
| 10 milligrams make | 1 centigram. |
| 10 centigrams make | 1 decigram. |
| 10 decigrams make | 1 gram. |
| 10 grams make | 1 decagram. |
| 10 decagrams make | 1 kilogram. |
| 10 kilograms make | 1 myriagram |
| 10 myriagrams make | 1 quintal. |
| 10 quintals make | 1 millier or ton. |
On the adoption of the metric system, the
French also reformed their currency, abolishing the
livre and
sous, and adopting the
franc, which it was decreed should weigh five grams, and be composed of 9 parts pure silver and 1 part alloy.
It is divided into 100 centimes.
This piece constitutes the basis of the
French coinage.
Measures of Area.
The unit of area is a square whose side is 10 meters.
It is called an are, and is equal to 100 square meters.
| Centiare (.01 are or square metre), | 1 1960 sq. yards = 1,550 square inches. |
| Are (sq.
decametre and unit), | 119.6033 sq. yards or 0.0247 acres=3.9536p. |
| Decare (10 ares), | 1,196.033 sq. yards or 0.2471 acres=39.536p. |
| Hectare (100 ares) | 11,960.33 sq. yards or 2.471 acres=2 a. 1 r. |
| 35.376p. |
Table.
| 100 centiares make | 1 are. |
| 10 ares make | 1 decare. |
| 10 decares make | 1 hectare. |
The
United States, however, led the way in decimal currency.
The metric system, though adopted in 1795, was not fully carried into effect until 1840.
It is now employed throughout a large part of Continental
Europe, and seems in a fair way to be generally adopted at some not very distant day in the
United States, where it may now be legally employed at the option of the parties interested.
