Time Measurement

Introduction

To 1790

The earliest form of timekeeping were the sundial, the hourglass, and burning candles.   These were inaccurate timers, but better than none when important conferences were to be held.   Crude sundials formed by a stick stuck in the soil was the first known form of timekeeping used by 4,000 BCE.   Circular bowl sundials that kept a shadow of constant length existed in Egypt by 700 BCE.   Sundials did not work when the sun was not out, so other ways of telling time were sought.   Later, water dripping from a top chamber to a bottom chamber marked with numbers to indicate the time of day.   Around 270 BCE, the Greek, Ctesibius, invented a water clock with a float attached to a rod and gear that pushed a pointer to indicate the numbers 1 to 12.   The water clock was an improvement over the earlier timing devices, but it was still pretty inaccurate. ^{Asimov 58}

The first mechanical clocks driven by weights pulled downward by gravity appeared in Europe in the late 13th or early 14th century.   Since these clocks had to be large and vertically mounted, they were mounted in city hall or church bell towers, a hand-pulled bell indicating the time of day.   These clocks were too inaccurate to tell the time to the minute.     Mechanical clocks powered by weights were used in towers in Milan, Italy by 1335.   Although no more accurate than the ancient water clocks, they were more convenient and eventually completely replaced them and led to further timekeeping inventions.   In 1504, a German locksmith named Peter Henlein invented a canister watch powered by a coiled mainspring, which was invented around 1470.   Galileo Galilei, the famous Italian scientist, discovered the constant action of the pendulum to produce nearly constant time intervals in 1581, although this principle would not be applied to clocks until 1656.   It was a crude instrument, because water level is also affected by atmospheric pressure, but it was an important beginning for measuring the hotness and coldness of objects.   The mercury barometer was invented by the Italian physicist, Evangelista Torricelli.   The pendulum clock was invented by the Dutch astronomer, Christiaan Huygens, in 1656.   It was the first clock that could tell time to the minute and was the first clock to be used by scientists.   Galieo's clock was improved by Christian Huygens in 1656 by adding a pendulum that moved at a constant rate.   Wound up by a spring, this constant rate of movement made clocks more accurate - to within a minute, or about 10 seconds per day.   This accuracy made clocks useful for scientific experiments. ^{Asimov 100-170}

About 1675, William Clement, an English clockmaker, devised an escapement for the pendulum known as the anchor or recoil escapement.   It substantially reduced the arc of the pendulum so that seconds could be calculated.   This improved the accuracy of clocks to about 15 minutes per day to 20 seconds per day. ^{How 536}

In 1721, George Graham, an English clockmaker, invented the mercury pendulum to compensate for temperature changes with a column of mercury on the pendulum that expanded to keep the same effective length. ^{How 537}

In 1761, John Harrison, an English carpenter, developed a watch with a balance wheel and compensated spring that was 5.1 seconds in error over 81 days.   It became famous because it was the first watch that was accurate enough to determine longitude in navigation .

1790-1799

1800-1809

1810-1819

1820-1829

1830-1839

In 1838, Chauncey Jerome of Bristol, CT, producted a mass-produced one-day brass clock for $2.00.   This price compared to $40 for a wooden clock, so the new clock wasw affordable to many more consumers.   Eventually, his factory turned out 600 clocks a day. ^{Carruth 205}

1840-1849

In 1840, Alexander Bain, a Scotsman, and Marwise, an English clockmaker, invented the first electric clock that worked off earth batteries, i.e., coke and zinc buried in the ground. ^{How 539}

In 1849, the first American watch company, the American Horologe Co., began production in Roxbury, MA.   Later, it will be renamed the Waltham Watch Co. ^{Schles 257}

1850-1859

In 1850, Aaron Lufkin Dennison began manufacturing the first 8-day watch.   However, its mainspring was too long, so it was abandoned and replaced by a 36-hour watch. ^{Carruth 235}

1860-1869

1870-1879

1880-1889

1890-1899

1900-1909

1910-1919

1920-1929

in 1921, an English engineer, W. H. Shortt, invented a free pendulum clock, partly electric, that kept time to within 0.1 seconds per year.

1930-1939

1940-1949

1950-1959

1960-1969

1970-1979

1980-1989

1990-1999