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Measuring your words – the SI Guide teaches the international language of science

Did you know you knew "techno-speak"? Most of us do – imperfectly, even though we are using this technical language every day. The chances are we don’t realize that we know it, but in any case, we would do well to learn it better. Here comes just what you need: a pocket dictionary of this "language": the SI Guide1).

The SI (International System of Units), a coherent, metric, and decimal system, is so much part of our mental framework that we never even stop to think about it, and yet, without it, the world would be a far less ordered place. ‘Coherent’, firstly, meaning that there are no other conversion factors except for one, 1. Then ‘metric’ meaning that it is based on invariable references, which cannot be destroyed, such as the circumference of the Earth, the duration of the day, the density of water, and the triple point of water. The SI is used in all contexts: in daily life, just as in the technical and scientific fields. Everywhere.

The ISO Handbook, Quantities and Units has proved its worth. It contains the 14 parts that go to make up ISO 31, Quantities and units, and that constitutes the body of International Standards covering the measurement of anything. Now we have a pocket version with just the essentials of the International System of Units in a handly manual of 32 pages.

The SI is built in such a way that only one unit is used for each kind of quantity, which makes the system very simple. But, of course, this SI Guide contains conversion factors for other common units, in order to make it easy to calculate numerical values expressed in SI units.

In this SI Guide, all the new SI prefixes are included; it also takes account of the recent decision by the Conférence Générale des Poids et Mesures (CGPM) to delete the class of supplementary units in the SI. The new units for logarithmic quantities, e.g., in acoustics (namely, the neper and the decibel), are equally included.

This SI Guide covers the basics of: the historical background, the principles of the SI, the base units, derived units, multiples and sub-multiples, additional units, printing rules, space and time, periodic phenomena, mechanics, heat, electricity and magnetism, light, acoustics, physical chemistry, atomic and nuclear physics activity, ionizing radiations, characteristic numbers, and it ends with conversion tables.

We are convinced that large number of people will benefit from the SI Guide in its small and practical format and at a special price for quantity purchases, because basically, everybody is involved; there are few professional or non-professional areas not concerned by the standards. The SI Guide provides excellent guidance and help for students in science and technology – and for their teachers – for

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engineers, technical writers, and for scientists. It will teach all of them to speak the international language of science. And those who require more detail will find it all in complete form in the ISO Standards Handbook.

Weigh it up – you’re certain to be a winner!

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What is the SI

What is the SI?History of the SI

IntroductionMilestonesBackground Giorgi's contribution The role of the IECResistance/AcceptanceGiorgi's life and work

The present situation in the IECContributors to the SIBinary multiples (kibi, mebi...)Examples of SI units used in IEC work

Electricity and magnetismLight

AbbreviationsBibliographyBack to SI zone homepage

Horizontal committees and functionsInformation on a Technical CommitteePublications and work in progress

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The International System of Units, or SI (from its French name Système international d'unités) is a system of metric weights and measures. It comprises, base and derived units.

Base units

Seven base units form the core of the SI:

the metre (m) for length; the kilogram (kg) for mass; the second (s) for time; the ampere (A) for electric current; the kelvin (K) for thermodynamic temperature; the mole (mol) for amount of substance; the candela (cd) for luminous intensity.

Derived units

Derived units are obtained in terms of the base units according to a system of equations relating the corresponding quantities. The SI derived units are obtained from the SI base units according to the International System of Quantities, or ISQ. The ISQ has all the time implicitly been the basis of the SI, but the concept ISQ has not until recently been explicitly recognized. For example, the SI derived unit of speed is metre per second (m/s), because the derived quantity speed in the ISQ is defined as length divided by time.

22 SI derived units have been given special names and symbols, such as newton (N = kg · m/s2) as the unit for force, including:

units for electricity: coulomb (C, for electric charge), volt (V, for electric potential and electric tension), farad (F, for capacitance), ohm (Ω for resistance) and siemens (S, for conductance); units for magnetism: weber (W, for magnetic flux), tesla (T, for magnetic flux density), and henry (H, for inductance); units for light: lumen (lm, for luminous flux) and lux (lx, for illuminance).

Additional units

In addition to the SI units, some additional units have also been adopted for international use, including:

units of time: minute (min), hour (h), and day (d); metric units used in everyday life: litre (l, for for volume) and tonne (metric ton, t, for mass).

Prefixes

In the SI decimal prefixes for multiples and submultiples, ranging from yotta (Y) 1024 to yocto (y) 10–24 are used.

IEC has also standardized prefixes for binary multiples (where kibi (Ki) means 210 = 1 024 instead of kilo (k) which means 103 = 1 000) in its International Standard IEC 60027-2, Letter symbols to be used in electrical technology — Part 2: Telecommunications and electronics.

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Introduction







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In October 1901, a very successful Italian scientist and engineer Giovanni Giorgi showed at the congress of the Associazione Elettrotecnica Italiana (A.E.I.) in Rome that a coherent system of units could be achieved by adding an electric unit to the three mechanical units (centimetre, gram, second) of the existing CGS system. The event can be considered as the birth of what is now known as the International System of Units, or SI.

The history surrounding the birth of SI is an example of how the world of international standardization can truly deliver a solution that meets past, present and future market needs.

The birth of SI is inseparably linked to the personality of Professor Giovanni Giorgi. This far-sighted Italian anticipated future needs and provided as early as 1901 not only suggestions for a coherent system of units, but a full-fledged solution. His case also shows that being ahead of one’s time can draw more criticism than being

behind. But fortunately, Giovanni Giorgi had the satisfaction of witnessing how, after many years of seemingly endless debate, his original proposals were accepted without major changes.

This saga is, however, not merely of historical interest. We know that specific styles of art, literature, technology, etc., tend to be superseded by later ones. Here again, Giovanni Giorgi’s legacy is exceptional. Far from being challenged by any better system, the SI (International System of Units) keeps proving its worth.

Readers may know that in Switzerland laws are not imposed by government and that even parliament does not have the power of final endorsement because this is the privilege of its citizens. In a similar way, the SI was accepted by the appropriate organizations, but a perfectly democratic vote took place and is still taking place in an informal but highly efficient way: this is the everyday use of Giovanni Giorgi’s system by the international engineering community.

All historical information presented in these pages comes from the book: "1901-2001, Celebrating the Centenary of SI - Giovanni Giorgi's Contribution and the Role of SI", published in 2001 by the IEC for the 100th anniversary of the International System of Units.

Examples of units (covering Electricity and magnetism, Light) come from ISO's SI Guide.

Copyright © IEC 2004. All Rights Reserved.

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Milestones







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In the middle of the 19th century, a coherent three-dimensional system of units was created using the base quantities length, mass and time. This was the absolute CGS system. The subsequent introduction of these absolute units into electrodynamics had many theoretical implications. Maxwell developed an elaborate metrological theory of two systems, the electrostatic and the electromagnetic system.

In 1901 Giovanni Giorgi succeeded in reformulating the existing theory of electromagnetic phenomena as a four-dimensional theory (Unità Razionali di Elettromagnetismo, Rational Units of Electromagnetism [1]).

The International Electrotechnical Commission (IEC) was founded in London in 1906 as an international forum where scientists and engineers could discuss all relevant questions.

In 1935 an IEC meeting in Scheveningen adopted a system comprising the three units metre, kilogram and second plus a fourth unit to be chosen later. This was called the Giorgi System.

IEC TC 25 (Quantities and units, and their letter symbols) was established.

In 1950 the ampere was finally chosen as the fourth unit of the system.

In 1960 the General Conference on Weights and Measures adopted a resolution that the system based on metre, kilogram, second, ampere, kelvin and candela be given the name Système international d’unités (International System of Units), with the abbreviation SI. In 1971 the mole was added as a seventh base unit.

It is shown why many physicists were opposed to the Giorgi System. In fact some theoretical physicists, though not engineers, still occasionally use the CGS system today.

Among the present projects of IEC TC 25 in the field of units, the future publication ISO/IEC 80000: Quantities and units, is particularly noteworthy. It is intended to harmonize all the relevant IEC and ISO International Standards.


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Historical background







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British Association for the Advancement of ScienceInternational Electrical CongressesInitiation of the IECThe contributions of Maxwell and Heaviside

British Association for the Advancement of Science

In 1862 the British Association for the Advancement of Science (BAAS) appointed the first Commission entrusted with the task of studying electric units. This commission consisted of physicists from various countries and with world-wide reputations, which gave it an undeniably international and authoritative character [2]. It undertook to extend work which had been initiated by the German scientists C.F. Gauss and W. Weber.

One of its first achievements, in 1863, was adoption of the system based on three fundamental units: metre, gram and second. When in 1874 the centimetre replaced the metre, the new system was named the absolute CGS system. Its use was universal until the introduction at the beginning of the 20th century of the MKSA system.

After adopting the CGS system the same commission also decided, in 1874, to adopt ohm as the unit for resistance and volt for electromotive force (emf). These so-called practical units had come into use because of the inconvenient size of some of the electric units in the CGS system.

The ohm was defined as 109 electromagnetic CGS units, close to the resistance of a column of mercury about 1 m long and of 1 mm2 cross-section. The volt was defined as 108 electromagnetic CGS units, close to the emf of a Daniell cell, commonly used at that time in laboratories. Furthermore, prefixes ranging from mega to micro were introduced for expressing multiples and sub-multiples.

After the important part played by the BAAS, the work of six International Congresses held between 1881 and 1904 contributed greatly to the unification of electric and magnetic units. The last Congress was held only a short time before the birth of the IEC.

Fundamental units are base units, as opposed to derived units.

Absolute measurements are based on the three-dimensional system of units. They are no longer relative measurements, that is based on comparisons.

The MKSA system uses metre, kilogram, second and ampere as base units.

Practical units are obtained by multiplying the absolute CGS units by integral powers of 10.

International Electrical Congresses

At the time of the first International Electrical Congress in Paris in 1881, there were in many countries no fewer than 12 different units of emf, 10

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different units of electric current and 15 different units of resistance.

The principal result of this first congress was to give official and international endorsement to the BAAS proposal concerning the ohm and the volt. The ohm was now defined as “the resistance of a column of mercury of 1 mm2 cross-section and 106,300 cm long at the temperature of melting ice”. The units ampere, coulomb and farad were also defined.

In addition to these definitions in terms of conceptual representation, the first Paris congress gave its attention to the material representation of these units [3].

Later congresses were held in 1891 (Frankfurt), 1892 (Edinburgh), 1893 (Chicago), 1900 (again in Paris) and 1904 (St. Louis). The Chicago congress laid down rules for the physical representation of the three principal units: ohm, ampere and volt. Ohm and ampere were defined in terms of the CGS electromagnetic system.

The Congress in Paris in 1900 dealt mainly with the contentious question of magnetic units.

Initiation of the IEC

When the next Congress met in St. Louis, the IEC was initiated [2]. In fact, two permanent international commissions were proposed with different sets of tasks:

to make a study of electric units and standards; and to study the unification of nomenclature and of the characteristics of electrical machines and apparatus.

Obviously, two distinct needs were specified at the time. First, the governments saw that it had become necessary for commercial transactions and trade to take quick, official and common action about the very different units that were in use. Secondly, it appeared to be necessary to provide a forum that would consist of scientists and in which manufacturers as well as learned societies would be represented. Its responsibility would be to study and to establish terminology for the whole field of scientific and technical concepts [2].

The contributions of Maxwell and Heaviside

The mathematical theory of electromagnetic phenomena had been formulated on a three-dimensional basis by J.C. Maxwell in 1873 but, despite many qualities, his presentation was in some respects arbitrary [3]. In particular, he developed two systems as extensions of the CGS system into the field of electricity, the absolute electrostatic system and the absolute electromagnetic system. They are respectively based on:

choosing the permittivity in Coulomb’s law to be dimensionless and equal to 1; and choosing the permeability in the law of magnetic interaction to be dimensionless and equal to 1.

If a given physical quantity is measured in the two different systems of



units, however, it has not only different numerical values but also different dimensions. These facts were pointed out in 1882 and later by O. Heaviside.

Heaviside’s most important objections [3] were that, in the case of both electricity and magnetism, the electric field strength and the corresponding flux density must be quantities with different dimensions. Rather than pure numbers, the permittivity and the permeability were quantities with a dimension. This means that Heaviside’s presentation refers in fact to four dimensions. Heaviside also criticised the irrational way in which the factor 4π occurs or does not occur in the mathematical formulas, implying that it should appear only in equations concerning spherical geometry. He proposed to redefine the electrical and magnetic units by making these smaller by a factor of , keeping the vacuum permittivity and vacuum permeability invariant. Of course, this procedure would have dramatic consequences for other quantities.

At the beginning of the 1890s, the Italian scientist and engineer Giovanni Giorgi realized the great importance of Heaviside’s ideas.




Giovanni Giorgi's contribution to the SI







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Giorgi was also a firm supporter of rationalization. His careful approach required only a minimum of changes in existing unit conventions. He did not modify the definitions of electric charge or magnetic flux, limiting changes to those for permittivity, permeability, electric flux density and magnetic field strength. This led to a highly satisfactory solution, including the rationalization aspect, and won general acceptance for the four-dimensional description of electromagnetism.

Giorgi’s contribution relates therefore essentially to four items:

unification of the electrostatic and electromagnetic systems; elimination of the need for conversion factors; elimination of the fractional exponents from dimensional equations; the conclusion that permittivity and permeability are physical quantities with dimensions (with the units F/m and H/m).

Giorgi’s all-embracing proposals to reformulate the theory of electromagnetic phenomena as a four-dimensional theory, to rationalize the equations and to integrate practical and MKS units in a single four-dimensional unit system obtained a favourable response from many scientists, including S.P. Thompson. However, it would still take more than 30 years before these ideas were accepted by the responsible international organizations.

In Giorgi’s hands, the ideas of O. Heaviside became essential elements both for developing new logical descriptions of electromagnetic phenomena and for improving the system of units [3].

Already in 1896 Giorgi had criticized the peculiar dimensions of electrical quantities in the three-dimensional system. He agreed with Heaviside that permittivity and permeability expressed the physical properties of the medium. Disregarding their dimension led to strange situations, such as a resistance having the dimension of a velocity or its inverse, or a self-induction having the dimension of a length.

In Giorgi’s opinion, dimensions should express the true nature of a physical quantity. He saw the need to introduce – together with the base quantities length, mass and time – a fourth base quantity of electrical nature: “It is evident that by assuming the current as a fundamental concept, the definition of any other electromagnetic quantity easily follows.”

Giorgi also had the great merit of showing that the “absolute” system of practical units could be combined with the three mechanical units metre, kilogram and second to constitute a single coherent four-dimensional system of units. Four units – metre, kilogram, second and, for instance, ohm or ampere – could be chosen as base units from which all other practical electrical units could be derived. This proposition resulted in a harmonic synthesis of the practical electrical units with an acceptable set of mechanical units.

In an absolute system of practical units, the units are defined in terms of the mechanical units.

A coherent system of units means that the definition of the units avoids “useless coefficients”.

Rationalization includes giving physical dimensions to ε0 and µ0, and elimination of the factor 4π where it does not concern spherical geometry.

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The role of the IEC







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Founding of the IECWork on quantities and units

Founding of the IEC

The International Electrotechnical Commission saw its beginnings at the International Electrical Congress in St. Louis in 1904. It had been recommended "that steps should be taken to secure the cooperation of the technical societies of the world by the appointment of a representative Commission to consider the question of standardization of the Nomenclature and Ratings of Electrical Apparatus and Machinery" [5].

A preliminary meeting, chaired by A. Siemens, was held on 26 and 27 June 1906 in London under the auspices of the British Institution of Electrical Engineers.

Of the 16 participating countries, three came from outside Europe: America (as it was listed at that time), Canada and Japan. The delegates were appointed by their national institutions, provided that they already existed; otherwise, they were appointed by their governments.

Colonel Crompton, a mechanical engineer, inventor and skilled organizer, played an important part in setting up the organization.

On 27 June 1906, the official birthday of the Commission, the eminent physicist Lord Kelvin was elected its first President; Colonel Crompton was appointed Honorary Secretary.

Further results of the first meeting:

the Rules of the Commission were approved; the name of the Commission was amended to read International Electrotechnical (instead of Electrical) Commission; Ch. LeMaistre became the first General Secretary; the office of IEC was in London.

In the course of time, a much wider interest had developed in creating a coherent system of units

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for electricity; the unit of electrical nature was now under discussion [2]. Two "commissions" of the IEC were therefore created:

Electric units and standards; and Nomenclature and characteristics of electrical machines and apparatus.

It is interesting to note that the IEC was thus constituted within the same timeframe as the national bodies. This fact underlines both the high priority given to the electrotechnical standards and the close cooperation between national and international efforts.

Work on quantities and units

From the date of the creation of these commissions, those responsible for the two fields of standardization acted separately. The first commission on electric units and standards met in London in 1908. It dealt with the units and their physical representation.

The representatives of the national institutions or governments at this conference adopted a set of fundamental units, defined as decimal multiples of the corresponding electromagnetic CGS units, and another one forming a system to represent the fundamental units that was sufficiently close to the fundamental units to serve for purposes of measurement.

These international units were based on the “international ohm”, defined in terms of a column of mercury, and the “international ampere”, defined in terms of the deposition of silver by an electric current.

The IEC also began its work on terminology in 1908, in the first Technical Committee (TC 1) to be appointed. Its title was the “Advisory Committee on Nomenclature”.

It was not until 1927 that TC 1 dealt with the study of various outstanding problems concerning electrical and magnetic quantities and units. Discussions of a theoretical nature were opened at which eminent electrical engineers and physicists considered whether magnetic field strength and magnetic flux density were in fact quantities of the same nature. As disagreement continued, the IEC decided on an effort to remedy the situation. It instructed a task force to study the question in readiness for the next meeting.

After intensive correspondence among its members, the task force recommended (among other items) examination of whether it would be appropriate to select, side-by-side with the CGS system, an absolute and rationalized system for all the practical units. This could be the system proposed by Giovanni Giorgi in 1901 (metre, kilogram, second, international ohm) or the Dellinger-Bennett system (centimetre, 10–7 gram, second). Either system would have the advantage of abolishing the then existing set of electromagnetic and electrostatic units found in the CGS system. Either system would also avoid the need to introduce at every turn the troublesome coefficients c0, c0

2 or their reciprocals, c0 being the speed of propagation of electromagnetic waves in vacuum.

In 1930 in Stockholm, and based on the recommendations of the task force, TC 1 took the following decisions which were ratified in the same year in Oslo [2]:

that the question of names to be allocated to magnetic units should not be considered until general agreement had been reached on their definitions; that the formula B = µ0 H represents the modern concept of the physical relations for

magnetic conditions in vacuum; in this expression µ0 possesses physical dimensions;

in the case of magnetic substances, the above formula becomes B = µH, in which µ has the same physical dimension as µ0. It follows that the relative permeability of a magnetic substance is a number equal to µ / µ0.

These decisions were reinforced by proposals for the definition of the following magnetic quantities:

magnetic field strength; magnetic flux density; magnetic flux;



magnetomotive force; magnetic permeability.

The much discussed question of the difference between the nature of the quantities H, magnetic field strength, and B, magnetic flux density, was finally settled. TC 1 was now able to turn to two other most important questions: first, extension of the existing set of practical units into a coherent practical system of physical units; and secondly, rationalization of the electromagnetic field equations.

In 1931, TC 1 decided to subdivide its field of study into three categories:

Section A: Vocabulary Section B: Electrical and magnetic magnitudes and units Section C: Letter symbols.

In Paris in 1933, following discussion of a resolution of the American Committee of the International Union of Pure and Applied Physics (IUPAP), Section B of TC 1 submitted a resolution to replace the CGS system of units by a more practical system:

“Section B of the Advisory Committee No.1 on Nomenclature, having heard with great interest the communication from Mr. Giorgi on the MKS system, and endorsing the resolution adopted by the American section of the International Union of Pure and Applied Physics at Chicago in June 1933, decides to invite the National Committees to give their opinion on the extension of the series of practical units at present employed in electrotechnics by its incorporation in a coherent system having as fundamental units of length, mass and time, the metre, the kilogramme and second, and as fourth unit either that of resistance expressed as a precise multiple 109 of the CGS electromagnetic unit or the corresponding value of the space permeability of a vacuum.”

At the meeting in Scheveningen, in 1935, TC 1 took the almost unanimous decision, following on the proposal of its Section B, to adopt under the name of “Giorgi System” the system with four basic units comprising metre, kilogram and second plus a fourth unit to be chosen later.

In view of the importance of the questions dealt with by Section B, it was also decided in 1935 to entrust all questions concerning electrical and magnetic magnitudes and units to a special Study Committee to which the title “Advisory Committee on Electric and Magnetic Magnitudes and Units” was given with the number 24. The title by itself very briefly but clearly summarized the scope of TC 24.

In 1938, TC 24 held its first meeting in Torquay. This meeting was chiefly concerned with the problem of either choosing the fourth unit in the Giorgi system or finding a connecting link between the electrical and mechanical units of the same system. It recommended as a connecting link the permeability of free space with the value of µ0 = 10–7 H/m in the unrationalized system or µ0 = 4π

· 10–7 H/m in the rationalized system.

Also, the TC recognized that any one of the practical units already in use – ohm, ampere, volt, henry, farad, coulomb and weber – could equally serve as the fourth fundamental unit.

Unfortunately, the Second World War interrupted the work of the IEC, including that of TC 24. But, at its first post-war meeting held in Paris in July 1950, the committee finally settled the question of the choice of fourth unit by recommending the ampere.

A text adopted in 1956 prescribes the form in which the principal equations for the electromagnetic field are to be written and introduces into them the magnetic permeability µ0 and the permittivity ε0 of free space.

µ0 = 4π · 10–7 H/m

ε0 = (1/c02) · µ0 F/m

TC 24 also appointed a committee of experts to study the method of “total” rationalization, meaning rationalization both by quantities and by units. Their proposals were examined and approved by TC 24 and finally adopted by the IEC in July 1956.



Meanwhile, the tenth General Conference on Weights and Measures (CGPM) met in Paris in October 1954 and adopted the following base units [2]:

Length metre Mass kilogram Time second Electric current ampere

Thermodynamic temperature degree Kelvin 1)

Luminous intensity candela At a meeting in Paris in October 1960 the eleventh CGPM decided to name the system based on these units the Système international d’unités (International System of Units), with the international abbreviation SI.

In 1971, the fourteenth CGPM recognized the need for an additional base unit of the SI (the seventh): the mole is the unit of amount of substance.

1) The unit name "degree Kelvin" was replaced with "kelvin" by the thirteenth CGPM 1966/67




Resistance to and acceptance of the Giorgi system







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Statement by J.H. Dellinger (U.S. Bureau of Standards) in 1916Statement of R.T. Birge (USA) in 1935

The question arises why the acceptance of G. Giorgi’s proposal for a coherent unit system turned out to be such a slow process. C.H. Page (National Bureau of Standards, USA) sheds some light on this issue in his paper “The Giorgi System in the USA” [4].

Although it is not possible in the present account to provide many details, the following excerpts may help in understanding the background to the relevant issues.

Statement by J.H. Dellinger (U.S. Bureau of Standards) in 1916

“In conclusion, this study has shown that the international system, based upon representing the electromagnetic system, is a convenient and satisfactory system of units for the purposes of electric and magnetic measurements. Proposed changes in some or all of the units do not appear to offer advantages such as to justify the confusion and inconvenience of changing the units as ordinarily used.”

Statement of R.T. Birge (USA) in 1935

“The IEC seems to favor the theory of the absolute character of dimensions. Having voted that B and H were of different physical character, the IEC apparently assumed, without further debate, that they therefore necessarily had different dimensions; in other words, that their ratio possessed physical dimensions. If the entire scientific world could only realize clearly that the character of a physical quantity is a matter of philosophy, while the assigned dimensions of its unit are a matter of mere convention having only arithmetic significance, unending and utterly fruitless controversies would be avoided. Meanwhile, one can only hope that the point-of-view of the IEC will not be accepted by physical scientists.”

Finally, however, the SI was adopted by the IEEE in IEEE Standard 268, 1965, entitled “IEEE Recommended Practice for Units in Published Scientific and Technical Work”. This standard was deemed so important that it was published in the IEEE Spectrum, the only standard ever so honoured. An accompanying article also carried some remarks by L.E. Howlett, president of the CIPM, and in particular:

“The adoption of this system by the large and influential IEEE as the recommended one for all its publications is most gratifying, and particularly significant since the headquarters of the IEEE is located in North America, the last continental stronghold of the Imperial System. This action, coupled with that already taken by the U.S. National Bureau of Standards and similar steps under study by other American organizations, gives grounds for hope – nonexistent a decade ago – that the day is not far off when the 18th-century scientists’ dream of a universal measurement system will become a reality.”

Note: The CGS system is still used by certain physicists. This system, however, is absolutely inadequate for an electrical engineer who designs a turbine generator or an electric power transmission system.


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Giovanni Giorgi's life and work







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Giovanni Giorgi was born in Lucca, Italy, on 27 November 1871. He graduated in engineering in Rome in 1893. His accidental death occurred on 19 August 1950 at Castiglioncello.

Giorgi’s professional career was brilliant. Some highlights include:

Prof. Giorgi’s activities and interests reflect his broad cultural and scientific background, covering numerous but not necessarily related subjects:

Some of Giovanni Giorgi’s work of fundamental importance was fully appreciated only after many years. The best example of this is the slow process of acceptance of his proposal in 1901 for a coherent unit system. The page describing the present situation in the IEC shows that an enormous amount of technical knowledge is based, and will be based in future, on the SI which was developed from Giorgi’s original ideas. This knowledge extends well beyond the borderline of electrotechnology into all technical fields.

1897-1906 Manager of various electrical and mechanical equipment companies 1906-1921 Director of the technical department of the City of Rome From 1910

Lecturer, and later professor, in various scientific fields (University of Rome; School for Aeronautical Construction, Rome; Royal School of Engineering, Rome; Royal University of Cagliari; University of Palermo)

1935 and 1938 Italian Delegate in IEC meetings

Science and technology, e.g. the application of operational calculus to electromagnetism; contributions to pure and applied mathematics; analytical mechanics; relativity (including correspondence with Einstein).

The arts, one of his many contributions to the Enciclopedia Italiana concerning the use of colours in the Middle Ages and in modern art.

Engineering, where he was active in various technical fields such as urban and interurban electric traction, and electric power distribution systems.

Didactic issues, where he worked on methods of disseminating scientific and technical knowledge to the non-specialized public.

Publications, being the author of 350 scientific/technical papers and author or co-author of several text books on science and engineering, for example Verso L’Elettrotecnica Moderna, 1949. Libreria Editrice Politecnica, Milano.


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