Friday, May 13, 2011

Units of Measurement

Units of Measurement


The English system is composed of a lot of very sensible length units. Hands, feet, rods, paces — these are things I can relate to. Furlongs, fathoms, miles, yards — these make sense if you know a little bit of etymology (the study of the origins and evolution of words). Unfortunately, the conversion factors are a mess. Feet don't fit into furlongs in an easy to grasp way. There are a lot of "nice" numbers in this system — numbers like 3, 4, 5, 6, 8, 12 and 16 — but after awhile you begin to feel buried in the "special" numbers that arise from the combinatoric gyrations the system runs you through.


An inch is the length of three barleycorns placed end to end. The word inch comes from the Latin word for one-twelfth (uncia) since there are twelve inches in a foot. The inch is commonly subdivided into halves, quarters, eighths, sixteenths, and other powers of two; but can also be divided into hundredths (as in the caliber of firearms) or thousandths (called mils). One inch is now defined as 0.0254 m (or 2.54 cm if you prefer).


A hand is the width of a man's hand. Used to measure the height of horses and not much else. A standard hand is 4 inches.


A foot is the length of a man's foot — a convenient measuring tool for many purposes. (Convenient for men with feet, anyway.) A standard foot is 12 inches.


A yard is the length from the King's nose to his outstretched hand. Presumably, after the king held out his hand someone placed a stick in the gap and marked it. This stick would then be the standard stick of the kingdom. Yard is an Old English word for staff, rod, or stick. That makes the word yard-stick a candidate for the Department of Redundancy Department. A standard yard is 3 feet long.


The pace has its origins in Rome. The passus was measured from the heel of one foot to the heel of the same foot when it next touched the ground. This is a convenient unit for measuring walking distances (again, for men with feet). A standard pace is 5 feet long.


The fathom is a measure of length that was commonly used by navigators. It was the length to which a man could extend his arms while measuring ropes used to determine the depth of navigable waters. The word fathom has its roots in the Old English word for embracing arms. A standard fathom is 6 feet long


A rod is a measure of length equal to 16½ feet or 5½ yards. It is also called a pole or a perch. (I'd hate to see the size of the budgie that needed a sixteen and a half foot perch.)


Surveyors commonly used chains for measuring distances. The most famous of these was developed by the English mathematician Edmund Gunter (1581-1626). The links of Gunter's chain were each 792/100 inches long. One hundred links gave it a total length of 792 inches, 66 feet, or 22 yards. Not a sensible number if you ask me, but then I don't play cricket. (The distance between wickets on a cricket pitch is 22 yards.)


Literally, the length of a furrow. A sensible length for farmers that later evolved into the acre, which is discussed later in this section. A standard furrow is 220 yards long or ⅛ mile


One mile was the distance of a thousand paces: in Latin, mille passus. A pace being 5 feet gives a mile of roughly 5000 feet. The mile acquired its current value of 5280 feet (1760 yards) by the decree of the English parliament during the reign of Elizabeth I. Since this was a legal definition it became known as the statute mile — statute being another word for law.

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