English measurement system
The why of this way?
This article was originally published on August
25, 2017, by Mental Floss, and is republished here with permission.
The why of this way?
Why are there 5,280 feet in a mile, and why
are nautical miles different from the statute miles we use on land?
Why
do we buy milk and gasoline by the gallon?
Where does the abbreviation
"lb" come from? Let's take a look at the origins of a few units of
measure we use every day.
The Mile
The basic concept of the mile originated in
Roman times. The Romans used a unit of distance called the mille passum,
which literally translated into "a thousand paces." Since each pace
was considered to be five Roman feet—which were a bit shorter than our
modern feet—the mile ended up being 5,000 Roman feet, or roughly 4,850
of our modern feet.
If the mile originated with 5,000 Roman
feet, how did we end up with a mile that is 5,280 feet? Blame the
furlong. The furlong wasn't always just an arcane unit of measure that
horseracing fans gabbed about; it once had significance as the length of
the furrow a team of oxen could plow in a day. In 1592, Parliament set
about determining the length of the mile and decided that each one
should be made up of eight furlongs. Since a furlong was 660 feet, we
ended up with a 5,280-foot mile.
The Nautical Mile
So if the statute mile is the result of
Roman influences and plowing oxen, where did the nautical mile get its
start? Strap on your high school geometry helmet for this one. Each
nautical mile originally referred to one minute of arc along a meridian
around the Earth. Think of a meridian around the Earth as being made up
of 360 degrees, and each of those degrees consists of 60 minutes of arc.
Each of these minutes of arc is then 1/21,600th of the distance around
the earth. Thus, a nautical mile is 6,076 feet.
The Acre
Like the mile, the acre owes its existence
to the concept of the furlong. Remember that a furlong was considered to
be the length of a furrow a team of oxen could plow in one day without
resting. An acre—which gets its name from an Old English word meaning
"open field"—was originally the amount of land that a single farmer
with a single ox could plow in one day. Over time, the old Saxon
inhabitants of England established that this area was equivalent to a
long, thin strip of land one furlong in length and one chain—an old unit
of length equivalent to 66 feet—wide. That's how we ended up with an
acre that's equivalent to 43,560 square feet.
The Foot
As the name implies, scholars think that the
foot was actually based on the length of the human foot. The Romans had
a unit of measure called a pes that was made up of twelve smaller units called unciae. The Roman pes
was a smidge shorter than our foot—it came in at around 11.6 inches—and
similar Old English units based on the length of people's feet were
also a bit shorter than our 12-inch foot. The 12-inch foot didn't become
a common unit of measurement until the reign of Henry I of England
during the early 12th century, which has led some scholars to believe it
was standardized to correspond to the 12-inch foot of the king.
The Gallon
The gallon we use for our liquids comes from the Roman word galeta,
which meant "a pailful." There have been a number of very different
gallon units over the years, but the gallon we use in the United States
is probably based on what was once known as the "wine gallon" or Queen
Anne's gallon, which was named for the reigning monarch when it was
standardized in 1707. The wine gallon corresponded to a vessel that was
designed to hold exactly eight troy pounds of wine.
The Pound
Like several other units, the pound has Roman roots. It's descended from a roman unit called the libra. That explains the "lb" abbreviation for the pound, and the word "pound" itself comes from the Latin pondo,
for "weight." The avoirdupois pounds we use today have been around
since the early 14th century, when English merchants invented the
measurement in order to sell goods by weight rather than volume. They
based their new unit of measure as being equivalent to 7000 grains, an
existing unit, and then divided each 7000-grain avoirdupois pound into
16 ounces.
Horsepower
Early 18th-century steam engine
entrepreneurs needed a way to express how powerful their machines were,
and the industrious James Watt hit on a funny idea for comparing engines
to horses. Watt studied horses and found that the average harnessed
equine worker could lift 550 pounds at a clip of roughly one foot per
second, which equated to 33,000 foot-pounds of work per minute.
Not all scholars believe that Watt arrived
at his measurement so scientifically, though. One common story claims
that Watt actually did his early tests with ponies, not horses. He found
that ponies could do 22,000 foot-pounds of work per minute and figured
that horses were half again stronger than ponies, so he got the ballpark
figure of 33,000 foot-pounds of work per minute.
This article was originally published on August
25, 2017, by Mental Floss, and is republished here with permission.
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