Metre Convention
One hundred thirty years ago, on May 20, 1875, representatives of 17 industrially developed countries signed the "Diplomatic Document of the Metre Conference." We call this document the "Metre Convention" because its preamble states that the plenipotentiaries of several countries, "...desiring to ensure international unification and improvement of the metric system," decided to conclude a Convention for this purpose.
Interestingly, ministers, ambassadors, and envoys prevailed among the plenipotentiaries, and there were practically no scientific metrologists. But at the same time, the metrological level of the Convention turned out to be very high. Hence, the conclusion is that in the nineteenth century, the ruling circles paid great attention to the opinions of scientists. I would like it to be the same in the twenty-first century.
Many publications have been accumulated on the occasion of the next anniversaries since the signing of the Metre Convention. Indeed, it is hardly possible to name any other international agreements that have been in force for a long time. On the other hand, a certain algorithm for compiling such publications has been developed. They are all similar to each other and contain p
The development of metrology with the signing of the metric Convention did not stabilize, but even accelerated. First, thanks to F. Gauss, who proposed his absolute system in 1832, a third basic unit appeared - the second. Its appearance did not cause, apparently, any upheavals. Firstly, its presence was implied. This is at least based on the fact that one of the contenders for the role of the meter was the second pendulum, or rather, its length. There was a well-established astronomical service at one time. Speed, acceleration, and number of revolutions were measured quite professionally. The "non-systemic" nature of the second did not bother anyone. Secondly, after it was necessary to abandon the construction of a system based on a single basic unit, increasing the number was no longer fundamental.
After this, a period of developing various systems began, no longer measures but units of measurement, not without, in my opinion, some oddities. The first to appear was Gauss's already mentioned "absolute system of units" with the basic units: millimeter, milligram, and second.
Then the process of "system-creation" seemed to split into two, practically independent streams. According to Prigogine's terminology, metrology passed the bifurcation point. On the one hand, the metric system was systematically expanded and improved, gradually transforming from a system of measures into a system of units of measurement.
The first to be adopted were the ISS and MKSA systems in 1901, followed by the MSK (MKSKD, MKSLM) systems. One of the last, in 1919, was the MTS. There was also (only for mechanical quantities) the MKGSS. Finally, in 1948, the International Union of Pure and Applied Physics—IUPAP—proposed developing a unified international system of units of measurement. This system, now known as the SI, was adopted in 1960 at the XI CGPM.
Developing and adopting a large family of CGS systems marked the second parallel flow. Interestingly, these events took place "hot on the heels" of the metric Convention. These systems were developed in 1862-1870 by the Electrical Standards Committee of the British Association for the Advancement of Science and adopted by the First International Congress of Electricians (Paris) in 1881, just two years after the prototypes (standards) of the meter and kilogram were sent around the world. I could not find the sources of this situation anywhere. The initial skills of existence in a market system formulate a natural question: who lobbied for the CGS systems and benefited from them? I sacrifice this topic to a future historian of metrology. The situation is truly strange. At the same time, the metric system with its basic units - meter and kilogram - and a constellation of CGS systems with the corresponding units - centimeter and gram - operate. Moreover, no one even tries to create standards (measures) of the centimeter and gram (they will be less accurate than the metric ones). Roughly speaking, the CGS systems are parasitic on the metric system.
SI is formed according to the generally accepted method of constructing such systems, first applied in 1832 by K. Gauss when creating his "absolute" system of units. This method is as follows. Several basic units (if possible, independent of each other) are taken as the basis of the system, from which units of different quantities are derived as derivatives. Derived units are determined based on defining equations that link them with the basic and previously determined derivative units. It should be noted that any rules (algorithms) by which a particular set of units is selected as basic ones cannot be substantiated theoretically. The only criterion is the efficiency and expediency of using a given system. In practice, those units are chosen as basic ones that can be reproduced accurately.
The basic units of the SI are listed in the previous table. For a long time, the SI included two additional units – the radian and the steradian. Now they are classified as dimensionless derived units with their names (although, in principle, SI derived units cannot be dimensionless).
The main advantages of SI.
1. Unification of units of quantities. One unit and a clear system for forming multiples and submultiples are established for each amount.
2. SI covers all science, technology, and the national economy.
3. The main and most derived SI units have sizes convenient for practice.
4. The units of mass and force (weight) are clearly distinguished.
5. For all types of energy (mechanical, thermal, electrical, radiant, etc.), one common unit is established—the joule. Due to this, conversion factors such as the mechanical equivalent of heat, the thermal coefficient of work of electric current, etc., are unnecessary.
6. It is easier to write equations and formulas in various fields of science and technology. Significant time savings are achieved in calculations due to the absence of formulas compiled using SI units of conversion factors introduced because individual quantities in these formulas are expressed in different systems of units.
Limitations and disadvantages inherent in SI
The metric system of 1875 and SI, being universal in concept, are inevitably compromises, like any universal product. Some inconsistencies in SI, up to violations of the decimal principle of construction and "difficult relationships" between electrical and magnetic quantities, have been discussed repeatedly. I will not dwell on this. Much more significant is that SI applies only to quantitative properties - quantities that have proportionality. In terms of the theory of measurement scales, properties are described by scales of differences (intervals) and ratios. However, it does not apply to quantitative properties described by scales of order (which have no units). SI is perfectly compatible with absolute scale units, which are non-systemic, or more precisely, supra-systemic. No matter how much the creators and zealots of SI would like it to be, it is not the only one; the foot-pound-second system, dating back to the Ancient Babylonian duodecimal-sexagesimal systems of numeration and measures, is not going to give up yet. Moreover, the creators of metric systems had to come to terms with the sexagesimal-duodecimal construction of multiple units of time intervals - minutes, hours, days, months, and years. However, the second is the basic unit of SI.
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