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Page:Popular Science Monthly Volume 19.djvu/673

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ABOUT MEASURES OF LENGTH.

before completing it, and was succeeded by the Rev. R. Sheepshanks. That gentleman first constructed a bar of brass, which he found to measure 36·00025 inches, in terms of the lost standard. From this the present "imperial standard yard" known as "bronze 19" was made.

Before Sir Francis Baily died, he proposed the use of an alloy for standard measures, which is known as Baily's metal. It is composed of sixteen parts of copper, two and a half parts of tin, and one part of zinc. "Bronze 19" was made of Baily's metal; it is thirty-eight inches long, one inch wide, and one inch deep. The graduations are upon gold plugs that are sunk into the bar. The lines are sharp, and are very well adapted to accurate measurement; they are about 13000 of an inch in width. This standard was legalized by act of Parliament on July 30, 1855. The original standard "bronze 19," or, as it is also called, "No. 1," is kept in the "Strong Room" of Old Palace Yard. Four copies of it are in existence: one is at the Royal Mint, one is in charge of the Royal Society, one is in the new Westminster Palace, and the last is at Greenwich Observatory. Forty other copies were made in Baily's metal, and these have been distributed among different Governments, but only two of them are standard at the same temperature as the original.

From what has been stated, it will be observed that there is no natural unit from which our yard-measure has been derived; it is merely an assumed unit of length which has been declared a legal standard by the British Parliament.

The yard-measure of the United States, with which all measures to be verified are now indirectly compared, is known as "bronze bar No. 11," which was presented to the Government by the British Board of Trade in the year 1856. It is standard at 61·79 Fahr. It does not appear, however, that our Congress has ever sanctioned the use of this standard by any enactment. The only standard yard ever legalized by that body seems to have been a copy of a part of an old scale by Troughton, which had been used by the Treasury Department previously to 1856.

There is now a strong movement in favor of the general adoption of the French system of weights and measures in this country. The efforts that have been made to attain this very desirable result have met with great opposition, but this is steadily giving way before rational argument and sound elementary instruction, so that we may safely predict that our very irrational divisions of feet, inches, pounds, and ounces will eventually be abolished, and that a decimal system will take its place. There is a standard metre bar in the possession of our Government, but it has not been declared a standard by Congress, although it is used for comparisons.

The French metre was originally supposed to be equal to the one ten-millionth part of the quadrant of a meridian of the earth passing through Paris. An arc of a meridian which extends from Dunkirk to