Page:Origin of metallic currency and weight standards.djvu/282

 in 1824 and came into force on January the 1st 1826, by which certain measures and weights therein specified were declared to be the only lawful ones in this realm under the name of imperial weights and measures. It was settled by this Act (1) that a certain yard-measure, made by an order of Parliament in 1760 by a comparison of the yards then in common use, should henceforward be the imperial yard and the standard of length for the kingdom: and that, in case this standard should be lost or injured, it might be recovered from a knowledge of the fact that the length of a pendulum, oscillating in a second in vacuo in the latitude of London and at the level of the sea (which can always be accurately obtained by certain scientific processes), was 39·13929 inches of this yard: (2) that the half of a double pound Troy, made at the same time (1760), should be the Imperial Pound Troy and the standard of weight; and that of the 5760 grains which this pound contains, the pound Avoirdupois should contain 7000; and that, in case this standard should be lost or injured, it might be recovered from the knowledge of the fact that a cubic inch of distilled water at the temperature of 62° Fahrenheit, and when the barometer is at 30 in., weighs 252·458 grains: (3) that the imperial gallon and standard of capacity should contain 277·274 cubic inches (the inch being above defined), which size was selected from its being nearly that of the gallons already, in use, and from the fact that 10 lbs. Avoirdupois of distilled water weighed in air at a temperature of 62° Fahrenheit, and when the barometer stands at 30 in., will just fill this space. On p. 180 we saw that the standard gallon in the Tudor period ultimately depended on the pennyweight, which was, as we found, fixed by being the weight of 32 grains of wheat, dry and taken from the midst of the ear of wheat after the ancient laws of the realm. It was from the descendants of this gallon that the imperial gallon of 1824 was fixed, with a slight modification so as to make it contain 10 lbs. of distilled water weighed in air at a temperature of 62° and when the barometer stands at 30 in. The double pound Troy made in 1760 depended in like fashion for its ultimate origin on the wheat-grains, and it also affords us an interesting illustration of the doubling of the original single