 |
| |
| In the centuries succeeding Galileo, optical instruments
proliferated and increased in precision, making possible scientific discoveries
beyond the capabilities of the naked eye, from the galactic to the microscopic.
Shown above are specimens from the late 18th and 19th centuries: a Borda
reflecting circle, reflecting telescope, binocular microscope, and octant.
Jean Charles de Borda (1733-1799), a French mathematician and nautical astronomer, devised many instruments, among them a reflecting circle. Together with Delambre and Mechain, Borda used this to measure the length of an arc of a meridian between Dunkirk and Barcelona in 1790 . Borda, whose most significant work was done in hydraulics, strongly supported the introduction of the metric system and originated the word "metre" for its basic unit of length. |
 |
| The Royal Microscopical Society of Great Britain celebrated its 150th anniversary in 1989 with a set of stamps picturing objects magnified from 5 to 600 times: shown here are a blue fly, snow flake, blood cells, and a microchip. |
The metric system originated in France around the
time of the French revolution and was officially adopted in 1795. Louis
XVI authorized the formation of a commission, of which Lagrange was a
member, to reform weights and measures. Based mainly on decimal units,
it has been adopted as the standard system of measurement in science and
commerce throughout the world, except in a handful of countries, including
the United States, where it is legal and encouraged, but not mandatory.
The meter is the international unit of length; the General Conference
on Weights and Measures in Paris in 1875 was the occasion for the Treaty
of the Metre signed by 18 nations, including the U.S. The meter was originally
defined as one ten-millionth of the length of a quadrant meridian. In
1960 a wavelength of Krypton 86 radiation was used to redefine the meter;
the original platinum-iridium meter is still preserved in Paris. Since
1983, it is defined as the length traveled by light in vacuum during 1/299792458
of a second. The second, another standard, is defined as the time required
for 9,192631770 vibrations of a microwave emission line between the two
hyperfine ground levels of the cesium 133 atom. The advantage of these
standards lies in that they form a common basis for all scientific measurements,
and that they are founded on immutable physical properties of the cesium
atom.
|
 |
Metrication reached much of the English-speaking world in the 1970's, including former British colonies in Africa: Kenya, Uganda, and Tanzania. A set of four stamps illustrates the conversion between metric and other units currently in use; volume for gas at the pump, distance on the road, weights at the store, and temperature outside. Shown here is the temperature conversion stamp which graphically gives equivalent readings on the Fahrenheit and Celsius (here called Centigrade) scales for representative temperatures such as the freezing and boiling points of water, and the ambient outdoor temperature of 80 degrees F given as 27 degrees C, but rounded up from the actual conversion value of 26.5. Unfortunately, there is no stamp with a portrait of Daniel Gabriel Fahrenheit (1686-1736), a famous German instrument maker, who invented the alcohol and mercury thermometers, and who flourished in the Netherlands. He chose as the zero for his scale the temperature of a mixture of equal parts of ice and salt. The freezing point of water was then 32 degrees, and the boiling point of water 180 degrees higher, or 212 degrees. The Fahrenheit scale is still in use in the United States. |
 |
Charles-Edouard Guillaume (1861-1936) was a Swiss scientist who worked at the International Bureau of Weights and Measures for over fifty years, where he was responsible for calibration of thermometers and studies of thermal expansion of the standards of length, such as the International Meter. His discovery of a steel-nickel alloy called invar that was impervious to temperature changes advanced the development of precision instruments significantly. For this discovery and its many applications he received the 1920 Nobel prize in physics. |
A joint issue of France and Finland commemorates simultaneous 1736 French expeditions to the equator in South America and the polar regions of Lapland to determine the shape of the earth, generally acknowledged to be spherical. Charles LaCondamine (1701-1774) in Peru and Pierre Maupertuis (1698-1759) in Lapland surveyed the curvature of the meridians and found that the earth was somewhat flattened at the pole, and more curved at the equator, giving it the shape of an oblate spheroid.
This confirmed Newton's theory put forth in the Principia that
the centrifugal force of the rotating earth caused it to be distended
at the equator, where the speed of rotation was greatest, and flattened
at the poles, where the speed was zero - as indicated on the Finnish stamp.
Anders Celsius (1701-1744), the Swedish astronomer, was also a member
of the northern expedition. He was the inventor of the centigrade thermometer,
which divides the range in temperature between the freezing and boiling
points of water into 100 degrees. These divisions are now called degrees
Celsius. |
The question of the size of the earth continued to occupy the scientific minds of the 18th century, and soon after the measurement of the arc of a meridian by Delambre, Borda and Mechain in 1790, an even more ambitious project was conceived, this time in India. In 1799, Colonel William Lambton proposed a plan of a mathematical and geographical survey right across the subcontinent along the 78th E meridian, ostensibly to fix the location of some important points in the country, to aid surveyors in their work and to serve as reference points in a lattice for more detailed mapping. The method used was to be triangulation, and the survey was later called the Great Trigonometric Survey. Begun in 1802, by the time of Lambton's death in 1823 the Great Arc of the measured meridian extended for nearly 700 miles, or 10 degrees. Colonel George Everest took over the survey and completed the longitudinal aspects in 1866.
|
 |
| The zero meridian passing through Greenwich, England, has been used by international agreement since 1884 as the prime meridian for indicating longitude east and west on the earth, a reference for navigators and map makers. These British commemoratives show progressively smaller areas crossed by this imaginary line. |
 |
Since prehistoric times, calendars were devised to keep track of time - days, seasons, years. The Julian calendar introduced by Julius Caesar, based on the solar year and containing leap year, was succeeded by the Gregorian calendar, after minute discrepancies had accumulated over the centuries. Early Central American calendars had 18 months of 20 days, plus five days of bad luck. An Aztec calendar stone was the symbol of the 1968 Olympics in Mexico City. |  |
 |
The compass, a primary aid to navigation, has been known since ancient times; the one depicted on the Chinese stamp was used in the 3rd century BC. The modern compass rose is displayed on a German Red Cross commemorative. |  |
 |
This elaborate device is a seismograph, the work of Zhang Heng, an early Chinese astronomer. Inside the round jar is a pendulum which moves when an earthquake occurs, transferring its motion to one of eight rods, which in turn prods one of the eight dragons clinging to the outside of the jar. The dragons hold round balls in their mouths, disgorging them when struck. At the base of the jar sit eight toads with open mouths, ready to catch the dropping balls. The general direction where the earthquake took place is thus determined by the the toad holding a ball in its mouth. The name for this device is didongy. |
 |
| Navigation on charted or uncharted seas depended crucially on accurate, dependable time pieces in order to determine a ship's position based on the positions of celestial bodies. Many major disasters at sea were caused by faulty navigation due to inaccurate clocks that could not keep perfect time on pitching seas and in changing atmospheric conditions. The British Admiralty's Board of Longitudes offered a huge monetary prize for the successful development of a naval chronometer to determine longitude to within 60, 40, and 30 geographical miles at sea. John Harrison (1693-1776), a horologist, rose to the challenge and produced a series of five superb chronometers between 1736 and 1773, as the Board hedged on the reward, asking for more improvements. Harrison finally received his prize only after the intervention of King George III. |
| Last Modified: 2 April 2005 mn URL: http://ublib.buffalo.edu/libraries/asl/exhibits/stamps/meas.html Comments to: mnaylor@buffalo.edu Back to: Arts & Sciences Libraries © 1997, 2003 Maiken Naylor |
 |
