3.1 The Value of Defined Quantity Is the Quantity Expressed …
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used to make other derived units. Gauss was the first to make absolute measurements
of the Earth’s magnetic fields in terms of a decimal system. In the system proposed
by Gauss, units of all the physical quantities are expressed by a combination of three
base units: length, mass and time. Gauss called this system, the system of absolute
units. Initially, the system consisted of three base units: a millimeter, a milligram
and a second. Later, the system was based on the centimeter, gram and second. In
the following years, various changes were introduced and the system was expanded
by adding kelvin (K) as the unit of thermodynamic temperature, mole (mol) as the
unit of amount of matter and candela (Cd) as the unit of light.
During the development of a systems of units, two parallel trends were visible:
a 3D CGS system based on three units (base quantities): a centimeter, a gram, a
second; and a 4D system MKSA, which arose as a result of the development of the
metric system.
The metric system of units of measurement is older than the CGS system: the
former was originally designed for the measurement of length, area, volume and
weight, which were based on two units: length in meters (initially adopted as one
ten-millionth part of one-quarter of the meridian), and mass in kilograms (defined
initially as the mass of one cubic decimeter of distilled water at its maximum density).
The metric system was adopted in 1791 by the French National Assembly convened
in order to establish uniformity of measurement: in the second half of the nineteenth
century, it has become the international system. At the Diplomatic Treaty of 17
countries on May 20, 1875, the Metre Convention was created, whose task was to
improve international and state standards (etalons) of individual units of measurement
and organize the system of units in use. The focus of the Metre Convention was the
decimal metric system based on prototypes of meter and kilogram, as well as on
decimal division.
The BIPM has worked on the further development of the MKSA enforced in
countries that have signed the Metre Convention. At one of the sessions of the International Committee of Weights and Measures, a Commission emerged whose task
was to develop MKSA. The Commission proposed a system with an enlarged—compared with MKSA—number of base units, which also included: a unit of temperature
at absolute thermodynamic scale (kelvin) and the unit of luminous intensity (candela). This system was abbreviated as SI.
The BIPM approved the development of the Commission and submitted a draft of
the SI system to the International Organization of Legal Metrology (OIML), which
approved the project at a plenary meeting in Paris on October 7, 1958. In 1971, the
unit of the amount (number) of matter (mole) and derived units containing a mole
were included as base units and, therefore, became the SI units.
A major achievement of French science was the introduction for the first time of the
metric system based on standards of length (meter) and weight (kilogram), using the
principle of 10-fold multiples when creating secondary units. Incidentally, the artefact
realization of these secondary units was created, considered today as outdated. The
model of a meter is a platinum–iridium rod with a rectangular cross-section, the length
of which was designated as the distance between the leading planes of the rod, and was
one ten-millionth of the distance of a quarter of the Earth’s meridian passing through
25
used to make other derived units. Gauss was the first to make absolute measurements
of the Earth’s magnetic fields in terms of a decimal system. In the system proposed
by Gauss, units of all the physical quantities are expressed by a combination of three
base units: length, mass and time. Gauss called this system, the system of absolute
units. Initially, the system consisted of three base units: a millimeter, a milligram
and a second. Later, the system was based on the centimeter, gram and second. In
the following years, various changes were introduced and the system was expanded
by adding kelvin (K) as the unit of thermodynamic temperature, mole (mol) as the
unit of amount of matter and candela (Cd) as the unit of light.
During the development of a systems of units, two parallel trends were visible:
a 3D CGS system based on three units (base quantities): a centimeter, a gram, a
second; and a 4D system MKSA, which arose as a result of the development of the
metric system.
The metric system of units of measurement is older than the CGS system: the
former was originally designed for the measurement of length, area, volume and
weight, which were based on two units: length in meters (initially adopted as one
ten-millionth part of one-quarter of the meridian), and mass in kilograms (defined
initially as the mass of one cubic decimeter of distilled water at its maximum density).
The metric system was adopted in 1791 by the French National Assembly convened
in order to establish uniformity of measurement: in the second half of the nineteenth
century, it has become the international system. At the Diplomatic Treaty of 17
countries on May 20, 1875, the Metre Convention was created, whose task was to
improve international and state standards (etalons) of individual units of measurement
and organize the system of units in use. The focus of the Metre Convention was the
decimal metric system based on prototypes of meter and kilogram, as well as on
decimal division.
The BIPM has worked on the further development of the MKSA enforced in
countries that have signed the Metre Convention. At one of the sessions of the International Committee of Weights and Measures, a Commission emerged whose task
was to develop MKSA. The Commission proposed a system with an enlarged—compared with MKSA—number of base units, which also included: a unit of temperature
at absolute thermodynamic scale (kelvin) and the unit of luminous intensity (candela). This system was abbreviated as SI.
The BIPM approved the development of the Commission and submitted a draft of
the SI system to the International Organization of Legal Metrology (OIML), which
approved the project at a plenary meeting in Paris on October 7, 1958. In 1971, the
unit of the amount (number) of matter (mole) and derived units containing a mole
were included as base units and, therefore, became the SI units.
A major achievement of French science was the introduction for the first time of the
metric system based on standards of length (meter) and weight (kilogram), using the
principle of 10-fold multiples when creating secondary units. Incidentally, the artefact
realization of these secondary units was created, considered today as outdated. The
model of a meter is a platinum–iridium rod with a rectangular cross-section, the length
of which was designated as the distance between the leading planes of the rod, and was
one ten-millionth of the distance of a quarter of the Earth’s meridian passing through