Why a liter of water weighs a kilogram? Ten most important moments in the history of measurements

In any field of science there is such a large gap between the recognition and importance in Metrology. And it’s not the weather. Metrology is the science of measurements. She has a longer history than the modern Sciences were taught in the school and it is important for all the usefulness and power of science. No sound of Metrology there would be missions to the moon, modern medicine, self-driving cars, analysts of baseball and weather forecasts (good, anyway).

And even without science, Metrology for millennia has proven useful in the service of trade and Commerce, ensuring that the weight and the volume of production and other products can be standardized so as to make fraud and deception more difficult for fraudsters and cheaters.

What is Metrology and why is it necessary?

May 20 was marked the latest milestone in the long history of Metrology, when officially adopted a new definition of some of the most important units of science, including kilograms, the standard measure of mass. These changes reflect the revision of the so-called Le Système International d’unites (SI), the modern version of the metric system. In accordance with the instructions of the International Bureau of weights and measures, the SI has seven basic units from which to retrieve other units of measurement. In addition to pounds, some new base units include Kelvin (temperature), ampere (electric current) and mole (amount of substance). Remained unchanged the second (time), metre (length), and Candela (luminous intensity).

The latest upgrade to SI represents progress in science, but this is only the latest of several historical landmarks in the field of Metrology. Let’s consider ten most important turning points in Metrology.

The invention anatomical units (a long time ago)

Anatomical units appeared at the dawn of human civilization, perhaps at the time of the advent of agriculture. Of volume units such as “SIP” and “a handful”, was preceded by the emergence of “teaspoons” and “cups” and “pints”. In the case of length, the human “foot” or “step” appeared together with a man. At different times, from the ancient Egyptians to more recent contemporary society 1700 “ft” was equal to 10-14 inches.

Among other anatomical units of measurement were widely used “elbow”. His first mention came from the Middle East, also in the “Epic of Gilgamesh”, who was born in 2000 BC the Elbow as the measure of length was very comfortable in the construction of the ark.

And could be that the “double elbow” turned into the yard. King of England Henry I, who reigned 1100-1135 in years, tried to standardize the yard, defining it as the length from tip of nose to end of thumb (outstretched hand). In the end, the yard was three feet, a foot is 12 inches, the inch was defined as the length of three grains of barley, elongated in length. Anatomical unit of measurement was born out of Botanical.

The great Charter of liberties (Magna Carta), 1215

One of the most important documents in history has established the need for Metrology for the future of civilization and insisted that “in the whole Kingdom should be standard measures of wine, ale and corn,” and the same for weights. Over the next few centuries it worked through the stump-deck, but the principle was clear enough and metrologists, which came later, did a great job and achieved the goals set out in Magna Carta.

Queen Elizabeth I reformed the system of weights, 1588

Until her fleet was busy destroying the Spanish Armada, Queen Elizabeth I was busy with the establishment of more rational rules for weights and measures. Before that, English merchants had to deal with a bunch of different types of pounds, which had the pound “, avordupois“. The other “tower” pound was abolished by Henry VIII in 1527 in favor of the Troy pound for use in currency (so the lb is still the English currency, even when made of paper).

Elizabeth I set the standard pound avordupois for most applications, keeping the Troy pound coin (and drugs). However, she asked the smart question: what weighs more pound of gold or a pound of lead? Savvy often say: haha, neither. A pound is a pound. But those who are versed in Metrology, say “lead” because pound avordupois weighs more than a Troy pound. However, if you say that an ounce of lead weighs more than an ounce of gold, you will be mistaken. Troy ounce of gold is heavier. Pound avordupois heavier because it contains 16 ounces, a Troy pound is only 12 Troy ounces.

Pendulum clock by Christian Huygens in 1656 year

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

The metric system, in 1799

In the 17th century some visionary scientists have recognized that the decimal system of units will be much better for science and trade than then a hodgepodge of units that varied from country to country. Or even within the same country — some have suggested that one of the reasons the French revolution was the dissatisfaction of the people lack of uniformity of weights and measures.

In 1670-ies of the French cleric Gabriel Mouton, astrono Jean Picard discussed the creation of base units of length length of pendulum with period of 2 seconds. (It is relatively close to the modern meter, but, unfortunately, the rolling period of a pendulum varies in different areas of the Earth’s surface). But in 1790-ies, when the French began to think of the creation of the metric system, they identified the meter as 1/10 000 000 of the distance from the equator to the North Pole. Other units have gone from one meter — grams (mass unit) equated to the mass of cubic centimetre of water, for example.

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

The establishment of the International Bureau of weights and measures, 1875

Convention du Mètre in 1875, established the Bureau of weights and measures as the arbitrator to resolve the issues relating to units of measurement; the agreement was signed by 17 countries. The contract stated that the Bureau would undertake the manufacture of standard prototypes of the meter and the kilogram. This was an important step in the direction of wide use of the metric system worldwide.

Temperature scale Kelvin

Until the 19th century, temperature was a slippery concept — the thermometers used arbitrary units, which allows you to measure what the hot thing is another, but not allowed to determine whether it is hot. In 1848, William Thomson, becoming Lord Kelvin, proposed to apply the principles of a new science of thermodynamics to develop “absolute” temperature scale, which would set the zero point, corresponding to the complete absence of heat. It took some time before thermodynamics matured and it became clear the scale of what we need to do, but thermometry appeared solid Foundation. The unit of temperature was named in honor of Calvin, and were called Kelvins, not “degrees Kelvin” as before.

The Michelson Interferometer

Albert Michelson was obsessed with measuring the speed of light, and at the end of 1870-ies have measured it more accurately than anyone else. Soon after, he realized that can detect small differences in the speed of light caused by the motion of the Earth through the ether. For this he invented the interferometer. He divided a beam of light into two paths, perpendicular to each other, and then combined these two beams using mirrors. The speed difference between the two paths of light meant that light waves can be bent, creating the interference pattern. Michelson and his colleague Edward Morley conducted an experiment in 1887 failed to detect the expected interference. But it was due to the fact that the ether does not exist. Interferometry was a great idea and has become a valuable tool for various metrological tasks.

The discovery of lasers in 1960-ies has made interferometry an even more accurate thanks to the laser to control the wavelength of light. Thus, lasers not only secured the implementation of a science-fiction beamer, but quickly became the best tool of measurement in history. Lasers allow to create optical clocks which are thousands of times more accurate pendulum clocks of Huygens. Laser Metrology helped to confirm that the engines of aircraft and cars will be produced exactly according to design specifications.

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

Revision of the main units of measurement, 2019

In 1983, the kings of Metrology, redefined the meter in terms of a how far can light travel in a second. Thus began the redefinition of other units of measurement based on fundamental physics. Calvin, for example, is now defined constant based on the kilogram, meter and second. The kilogram is now defined by value of quantum physics — Planck’s constant — and the definitions of meters and seconds. The second is still based on the radiation emitted in a specific process of a certain cesium atom. Metrology is now not just standardized across the planet but for all planets in all galaxies, regardless of distance.

But the way to accurately measure the correct ranking of metrological benchmarks not yet invented, so you can do it. And don’t forget to check our chat in Telegram.

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