Metric system <TAG1> is an international system of measures based on the decimal principle and is the most common in the world. Its appearance is linked to the era of the French Revolution: in 1795, the meter, kilogram and other units created on the basis of universal and natural quantities were officially introduced in France. The purpose of the new system was to replace the many local measures that varied from region to region, creating a single, understandable and scientifically based system.
In the 19–XX centuries, the metric system gradually spread around the world. Today it is the basis International System of Units (SI), approved in 1960. In most countries, it is this system that is fundamental to measurements in science, technology, medicine, education and everyday life. For example, a meter is used for length, a kilogram — for mass, a liter — for volume, and a degree Celsius — for temperature.
How the designations were formed
1. Meter selection
It became the first basic unit meter. It was identified as one ten millionth of the distance from the equator to the North Pole along the meridian through Paris. This approach made the meter «a natural» value, not an arbitrary convention.
2. Decimal system
Instead of complex fractions (as in feet or inches), they decided to use them decimal principle:
1 meter = 10 decimeters
1 meter = 100 centimeters
1 meter = 1000 millimeters
That is, all divisions were built on numbers 10, because it is the most convenient for a person (we have 10 fingers). This was a revolution: earlier systems were often based on 12 (inches in feet, ounces in pounds, etc.), making computation difficult.
3. Liter and kilogram
Other units were derived from the meter:
Litre = cube volume with sides of 10 cm (ie 1 dm³).
Kilogram = mass of 1 litre of pure water at melting point of ice.
Thus, the basic units were interconnected and «logical»: length → volume → mass.
4. Prefixes
To denote larger or smaller multiples, a prefix system was introduced:
«kilo-» (1000),
«deca-» (10),
«deci-» (1/10),
«santi-» (1/100),
«mili-» (1/1000).
Later, «micro-», «nano-», «mega-» and others were added to the system. All of them were based on powers of the number 10, which ensured universality.
5. Why this is what the system looks like
The metric system looks just like that because its creators sought maximum simplicity and versatility:
decimal divisions <TAG1> most convenient for counting;
unity of units <TAG1> length, volume and mass are interrelated;
universal basis <TAG1> first because of the size of the Earth, and now because of fundamental physical constants.
This approach made it possible to make the metric system «a science language» and a convenient basis for international standards.
How the definition of meter and kilogram changed
First meter it was defined as one ten millionth of the distance from the equator to the North Pole along the meridian through Paris. Subsequently, a — standard platinum line with dashes was created for accuracy. In the 20th century, the definition was changed several times: first, the meter was tied to the length of the light wave, and from 1983, — to the speed of light in a vacuum.
A similar story with kilogram: it was based on a mass of 1 liter of water, later — on a platinum-iridium cylinder, and in 2019 finally «became disconnected from a physical object and began to be determined through fundamental physical constants (in particular Planck's constant).
Thus, the decimal structure remained unchanged, but standards were being refined according to the development of science.
Transition to the metric system: difficulties and curiosities
Despite the obvious advantages, the introduction of the metric system did not always go smoothly. In various countries, it was accompanied by resistance, curiosities and even political discussions.
Great Britain
In Britain, the metric system began to be gradually introduced from the 19th century, but the population held on for a long time to the traditional imperial measures. For example, pubs still serve beer in pints, and distances on road signs are measured in miles. At the same time, kilograms and liters are actively used in stores and in production. This led to a kind of «double life» measurement system.
United States
In the USA, US custom system (feet, inches, pounds, gallons) is officially used. Although Congress passed the «Metric Conversion Act» back in 1975, which was supposed to stimulate the transition, public opposition was so strong that the process effectively stopped. Americans are used to their measures and even consider them «more human» because a pound or an inch is easier to imagine. However, in science, medicine and the military sphere, the USA still uses the metric system.
It is interesting that in 1999 NASA lost the device Mars Climate Orbiter worth $125 million precisely because of the confusion in units: one group of engineers used pounds of force and the other – newton seconds (metric units). As a result, the calculations turned out to be incorrect, and the probe entered the atmosphere of Mars at too sharp an angle and burned up.
Canada and Australia
Canada officially switched to the metric system in the 1970s, but parallel uses can still be found: gasoline is sold in liters, but in everyday life people sometimes talk about height in feet or weight in pounds. Australia took a more decisive step — there the metric system completely replaced the old units already in the 1980s.
Other countries
In a number of African and Asian countries, the transition to the metric system was also not easy. Locals often kept traditional household-related units (such as «pumpkin» as a grain measure or «basket» for fruit). This created parallel systems that gradually disappeared only under the pressure of international trade.
