The Ration-ale of the Imperial Sy stem.—Take a pendulum which will vibrate seconds in London, on a level of the sea, in a vacuum ; divide all that part thereof which lies between the axis of suspension and the centre of oscillation into 391.303 equal parts ; then will ten thousand of those parts be imperial inch, twelve whereof In:die a foot, and thirty six whereof make a yard.
The Standard riled is "that distance between the centre of the two points in the gold studs in the straight brass rod, now in the custody of the clerk of the House of Commons, whereon the words and figures 'standard yard, 1760,' are engraved, which is declared to be the genuine standard of the measure of length called a yard ; and as the expansibility of the metal would cause some variation in the length of the rod in different degrees of temperature, the act determines that the brass rod in question shall be of the temperature I if 62 degrees Fahrenheit. The measure is to be denominated the • imperial standard yard,' and to be the only standard whereby all other measures of lineal extension shall be com puted. Thus the foot, the inch, the pole, the fachmy, and the mile, .shall bear the same proportion to the imperial standard yard as they have hitherto borne to the yard measure in general use." The act also makes provision for the restoration of the standard yard, in case of loss, destruc tion, or detlieement, by reference to an natural standard, which is to be that proportion which the yard bears to the length of a pendulum vibrating seconds of time in the latitude of London, in a vacuum at the level of the sea, which is found to be as 36 inches (the yard) to 391.393 (the pen dulum); thus a sure means is established to supply the loss which might by possibility occur.
Take a cube of one such inch of distilled water at 62° of temperature by Fahrenheit's thermometer ; let this be weighed by any weight, and let such weight be divided into 252•458 equal parts, then will one thousand of such parts be a troy grain ; and seven thousand of those grains will be a pound avoirdupois, the operation having been performed in air. Ten pounds such as those mentioned, of distilled water, at 62° of temperature, will be a gallon, which gallon will contain two hundred and seventy-seven cubic inches, and two hundred and seventy-four one-thousandth parts of another cubic inch.
The Standard Pound is determined to be that standard pound troy weight made in the year 175S, in the custody of the clerk of the I louse of Common*. : such weight is to be denominated the "imperial standard troy pound ;" and after the first of May, 1825, is to be "the only standard measure of weight, from which all other weights shall be derived, computed, and ascertained, and that one twelfth part of the said troy pound shall be an ounce, and one twentieth part of such ounce shall be a pennyweight, and that one twenty-fourth part of such pennyweight shall be a gra/n. ; so that 5760 such grains shall be a pound troy, and 7000 such grains shall be declared to be a pound avoirdupois, and one sixteenth part of the said pound avoirdupois shall be an ounce avoir dupois, and one sixteenth part of such ounce shall be a drachm." If the standard pound shall be lost, destroyed, or deflect], the act directs that it shall be recovered by reference to the weight of a cubic inch of water : it having been that a cubic inch of distilled water, weighed in air by brass weights, at the temperature of 62° Fahrenheit, :111d the barometer at 30 inches, is equal to 25•••158 grains ; and, as the standard troy pound contains 5760 such grains, it is therefore established that the original standard pound may be at any time recovered by making another weight to bear the proportion just mentioned to a cubic inch of water.
The Standard Gallon is determined by the act to be such measure as shall contain ten pounds avoirdupois- of distilled water, weighed in air, at the temperature of 62° Fahrenheit, and the at 30 inches, and such measure is declared to be the " imperial standard gallon, and shall be the unit and only standard measure of capacity to be used, us well for wine, beer, ale, spirits, and all sorts of liquids, as for dry goods not measured by heaped measure ; and that other measures shall be taken in harts, or multiples, of the said standard gallon—the quart being the fourth part of such gallon, and the pint one eighth part—two such gallons making a peck, eight such gallons a bushel, and eight such bushels a quarter of corn, or other dry goods not measured by heaped measure.