Why does a liter of water weigh a kilogram? Ten important moments in the history of measurement

No area of ​​science is so bigthe gap between recognition and importance, as in metrology. And it's not about the weather. Metrology is the science of measurement. It has a longer history than modern science taught in school, and this is important for all the utility and power of science. Without sound metrology, there would have been no flights to the moon, modern medicine, self-driving cars, baseball analysts and weather forecasts (good, anyway).

And even without science, metrology forFor millennia, it has proven its worth in the service of trade and commerce, ensuring that weights and production volumes and other products can be standardized to make fraud and deception more difficult for fraudsters and cheaters.

What is metrology and why is it needed?

May 20 was marked by the last frontier in the longthe history of metrology, when officially adopted the new definitions of some of the most important units of measurement of science, including kilograms, the standard measure of mass. These changes reflect the revision of the so-called Le Système International d’Unites (aka SI), the modern version of the metric system. In accordance with the guidelines of the International Bureau of Weights and Measures, the SI includes seven “fundamental” units of measure from which other units of measure are extracted. In addition to the kilogram, the new defined base units of measure include kelvin (temperature), amperes (electric current) and mol (amount of substance). The second (time), meter (length) and candela (luminous intensity) remained unchanged.

The latest SI upgrade isprogress in science, but this is only the last of several historical landmarks in the field of metrology. Let's look at the ten most important turning points in metrology.

The invention of anatomical units (long ago)

Anatomical units appeared onthe dawn of human civilization, perhaps at the time of the emergence of agriculture. Units of volume measurement, such as “sip” and “handful”, preceded the appearance of “teaspoons”, “cups” and “pints”. In the case of length, a human "foot" or "step" appeared together with a person. At various times, from the ancient Egyptians to the later modern society of the 1700s, the "foot" was 10-14 inches.

Among other anatomical unitsThe “elbow” was widely used. The first mentions came from the Middle East, also in the Epic of Gilgamesh, which was born in 2000 BC. The elbow as a measure of length was very convenient in the construction of arks.

And it may be that "double elbow"turned into a yard. King Henry I of England, who ruled in 1100-1135, tried to standardize a yard, defining it as the length from the tip of the nose to the end of the thumb (with an outstretched hand). Ultimately, the yard became three feet, foot - 12 inches, an inch was defined as the length of three barley grains elongated. Anatomical unit of measurement was born from the botanical.

Magna Carta Magna Carta, 1215

One of the most important documents in history.established the need for metrology for the future of civilization, and insisted that "throughout the kingdom there should be standard measures of wine, ale and corn", and the same for scales. Over the next few centuries it worked through the stump-deck, but the principle was clear enough and the metrologists, who came later, did an excellent job and achieved the goal set in Magna Carta.

Queen Elizabeth I Reforms the Scale, 1588

While her fleet was engaged in the destruction of the SpanishArmada, Queen Elizabeth I of England was busy setting more rational rules for weights and measures. Prior to that, the British merchants were dealing with a bunch of different types of pounds, of which the pound "averdupoys". The other — the “tower” pound — was abolished by Henry VIII in 1527 in favor of the troy pound for use in currency (therefore, pounds are still the English currency, even when made of paper).

Elizabeth I established the standard poundfor the majority of applications, saving troy pound for coins (and drugs). However, she asked people a smart question: what weighs more, a pound of gold or a pound of lead? Intelligent often answer: haha, neither one nor the other. Pound is pound. But those who are sufficiently versed in metrology will say “lead”, because a pound of averduction weighs more than a troy pound. However, if you say that an ounce of lead weighs more than an ounce of gold, you will also go wrong. Troy ounce of gold is heavier. Pound averdupe is heavier because it contains 16 ounces, and in troy pounds only 12 troy ounces.

Pendulum clock of Christian Huygens, 1656

Many (among them, and Galileo) tried to turnwith pendulums as a clock, but the Dutch physicist and mathematician Christian Huygens built the first reliable pendulum clock. Its earliest version, built in 1656, worked with an accuracy of 15 seconds per day, which is the biggest improvement for those times. The further development of the pendulum clocks made them the most accurate clocks until the 20th century.

Metric system, 1799

In the 17th century, some shrewd scientists recognizedthat the decimal system of units of measure would be significantly better for science and commerce than the then jumble of units that varied from country to country. Or even within the same country - some suggest that one of the reasons for the French Revolution was people's dissatisfaction with the insufficient uniformity of measures and weights.

In the 1670s, a French clergymanGabriel Mouton and astrono Jean Picard discussed the creation of a basic unit of length with a pendulum length with a period of 2 seconds. (This is relatively close to the modern meter, but, unfortunately, the rolling period of the pendulum differs in different places on the surface of the Earth). But in the 1790s, when the French seriously thought about the creation of the metric system, they designated the meter as 1/10 million distance from the equator to the North Pole. Other units of measurement have already gone from meter to gram (unit of mass) equated to the mass of a cubic centimeter of water, for example.

The metric system had its flaws, butit made the measurement much more rational and standard than it was before. Today, only backward countries (such as Liberia, Myanmar and one more) do not use SI (System International).

Establishment of the International Bureau of Weights and Measures, 1875

Convention du Mètre established a bureau in 1875measures and weights as an arbiter for resolving issues relating to units of measurement; The agreement was signed by 17 countries. The contract stated that the bureau would undertake the production of standard prototypes of meter and kilogram. This was an important step towards widespread use of the metric system around the world.

Kelvin Temperature Scale

Until the 19th century, temperature was a slippery concept -Thermometers used arbitrary units of measurement, which made it possible to measure which thing was hotter than another, but did not allow us to determine how hot it was. In 1848, William Thomson, becoming Lord Kelvin, proposed to apply the principles of the new science of thermodynamics to develop a rational "absolute" temperature scale that would establish a zero point corresponding to the complete absence of heat. It took some time before thermodynamics matured and it became clear what scale needed to be done, but thermometry had a solid foundation. Temperature units were named after Kelvin and became known as Kelvin, and not “Kelvin degrees,” as before.

Michelson Interferometer

Albert michelson was obsessed with measuringthe speed of light, and in the late 1870s, measured it more accurately than anyone else. Soon after, he realized that he could detect small differences in the speed of light caused by the movement of the Earth through the ether. For this, he invented the interferometer. He divided the beam of light into two paths, perpendicular to each other, and then connected the two beams with the help of mirrors. The difference in speed between the two paths of light meant that the waves of light could bend, creating an interference pattern. Michelson and his colleague Edward Morley conducted an experiment in 1887 and could not detect the expected interference. But this was due to the fact that the ether does not exist. Interferometry was a great idea and became a valuable tool for a variety of metrological tasks.


The discovery of lasers in the 1960s madeInterferometry is even more accurate due to laser control of the wavelength of light. Thus, lasers not only ensured the realization of science fiction ray-throwers, but also quickly became the best measurement tool in history. Lasers made it possible to create an optical clock that is thousands of times more accurate than Huygens' pendulum clock. Laser metrology helped confirm that the engines of airplanes and automobiles will be manufactured exactly according to the design specifications.

In addition, laser interferometry is used to detect gravitational waves.

Revision of the basic units of measurement, 2019

In 1983, the kings of metrology revised the meter withterms of how far light can travel per second. This was the beginning of the redefinition of other units of measurement, based on fundamental physics. Kelvin, for example, is now defined by a constant based on kilogram, meter and second. The kilogram is now determined by the value of quantum physics - the Planck constant - and the definitions of meter and second. Seconds are still based on the radiation emitted in a particular process of a particular cesium atom. Metrology is now not just standardized across the planet - but across all the planets in all galaxies, regardless of distance.

But we have not yet come up with a way to accurately measure the accuracy of the ranking of metrological reference points, so you can do it. And do not forget to look into our chat room in Telegram.