It is multiplied by 10 for the decametre, by 100 for the hectometre, by 1000 for the kilometre, by 10,000 for the myriametre. Practically the kilometre, = 0·621 mile or 1093·6 yards, is the only larger unit used; the other units are useless. And though it be interesting to know that the kilometre is approximately 1/10,000 of the quarter-meridian, it is a useless fact.
The square metre = 1·196 square yard. The lower units are little used. For land-measurement the square decametre, 10 × 10 metres, is called an Are; 100 ares = 100 × 100 metres, make a Hectare = 2·47 acres; and the square metre is a Centiare.
The cubic metre = 35·315 cubic feet (nearly the volume of a ton of water = 35·84 cubic feet) contains 1000 cubic decimetres, each of 1000 cubic centimetres (= 61 cubic inches).
The cubic centimetre is strictly speaking 1/1000 cubic decimetre, but as used in chemistry for fluid measure it is considered as 1/1000 of the litre, which is only approximately a cubic decimetre.
The Litre was originally a cubic decimetre, but this definition has been abandoned. It is now defined as the volume of a kilogramme of pure water in air at 4 degrees Centigrade = 39·2° Fahrenheit.
At ordinary temperatures a litre of water weighs about 998·8 grammes or 0·9988 kilogramme (see Table at end of Chap. X).
The only minor unit practically used (and only in scientific work) is the millilitre, under the name of cubic centimetre, = 15·432 grains of water.
1 Pint = 0·568 litre; 1 gallon = 4·546 litres.
The principal larger unit is the Hectolitre = 22·04 gallons or 2·75 bushels. The Decalitre = 2·2 gallons.
1 Bushel = 36·37 litres; 1 Quarter 291 litres or nearly 3 hectolitres.
1 Bushel to the acre = 0·9 hectolitre to the hectare. (Deduct 1/10 on English.)
1 Hectolitre to the hectare = 1·11 bushel to the acre. (Add 1/10 to French.)
The original unit was the Gramme, defined as the weight of a cubic centimetre of water at 4° Centigrade = 15·432 grains. It is divided into 10 decigrammes, 100 centigrammes, 1000 milligrammes. Of its multiples the decagramme is useless; the hectogramme is merely the name inscribed on a 100-gramme weight; the kilogramme of 1000 grammes is used when its use cannot be avoided.
But the present legal unit is not the gramme but the kilogramme = 2·2046 lb. or 15,432 grains.[51]