Milestones:Rationalization of Units, 1901-1902


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Giovanni Giorgi's Contribution to the Rationalized System of Units, 1901-1902


Giovanni Giorgi proposed rationalizing the equations of electromagnetism. His proposal added an electrical unit to the three mechanical units of measurement (meter, kilogram, second). While he was a professor at the University of Rome, the International Electrotechnical Commission adopted a version of Giorgi’s system. His ideas formed the basis of the universally adopted International System (SI) of units, currently used in all fields of science and engineering.

Street address(es) and GPS coordinates of the Milestone Plaque Sites

Via Eudossiana 18, 00184 Rome, Italy Latitude 41.889187Longitude 12.498257200000012, Via Eudossiana 18, 00184 Rome, Italy Latitude 41.889187Longitude 12.498257200000012

Details of the physical location of the plaque

The mounting is predicted in the ground floor entrance hall

How the plaque site is protected/secured

The plaque will be freely accessible to the public. During the opening hours, staff in charge is always present. A night watchman is provided as well.

Historical significance of the work

The mechanical-centered vision of physics, dominant for nearly all of the 19th century, implied that all the physical phenomena could be explained by the fundamental concepts of mechanics: mass, length and time. This choice seemed sound but, in this way, all the electromagnetic units had to be derived from the mechanical ones in a rather awkward way. However, this absurd assumption caused a great confusion in the field of the systems of units, a confusion which was solved only by the proposal of a new system by the Italian engineer Giovanni Giorgi at the beginning of the 20th century. Carl Friedrich Gauss (1777–1855) was the first to formulate the concept an “absolute system,” a system in which the values of the units do not vary from place to place, as it happens, for example, for the kilogram-force. In his system, all of the units were derived from the three fundamental units of length, mass, and time (millimeter, milligram, and second). In particular, the units for the electrostatic quantities were defined through the first Coulomb law with ke=1. Usually, two other conditions are required from an absolute system: the number of the fundamental units should be small enough and the secondary units should be defined by formulas without spurious numerical coefficients. The work of Gauss was continued by Wilhelm Eduard Weber (1804–1891). Weber showed how absolute measurements of resistance could be made by reducing all electrical magnitudes to measurements of mass, length, and time. The Gauss–Weber system was soon followed by many other absolute systems, relying on a different choice for the fundamental units, which were anyway always three in number and mechanical in nature. Then, during the International Exposition of Electricity held in Paris, the I Congrès International des Electriciens, took place, from 15 September to 5 October 1881. This congress was attended by approximately 250 delegates representing 28 countries. Among them were Hermann von Helmholtz, Rudolf Clausius, Gustav Kirchhoff and Ernst Werner von Siemens (Germany), Ernst Mach (Austria), Lord Kelvin and Lord Rayleigh (England), and Henry Augustus Rowland (United States). The importance of this congress can be understood if we remember that, at the time, there were 12 units of electromotive force, ten units of current intensity, and 15 units of electrical resistance used in different countries. Giorgi’s brilliant intuition was that all the difficulties could be solved simultaneously if one abandoned the absurd pretension of reducing the electromagnetic units to mechanical ones. His fundamental observation was that the group of units more used in practice — those of resistance, capacity, intensity of electric current, difference of potential, and inductance — is fully determined by just one of them taken as fundamental, plus the two units of work and time, the choice being independent from the units of length and mass provided that the electrical and mechanical powers are both to be measured in watts.

Features that set this work apart from similar achievements

A proposal of rationalization—i.e., the elimination of the annoying 4π factor—had indeed been made by Heaviside (1850–1925) some years before. He proposed to reformulate the Coulomb laws and assign to ke and km the values 1/(4πε) and 1/(4πµ), respectively. He even proposed some new units, which were different from the old ones by ratios of 2sqrt(π), 2, or 4π. However, the proposal, which came only six years after the international adoption of the practical units, was rejected. There was a long epistolary exchange between Heaviside and Giorgi.

Significant references

G. Giorgi, “Unità razionali nell’elettromagnetismo [Rational units in electromagnetism],” Atti dell’Associazione Elettrotecnica Italiana, vol. 5, pp. 402–418, Oct. 13, 1901.

G. Giorgi, “Memoria originale dell’ing. Giovanni Giorgi [An original memoir by Giovanni Giorgi, engineer],” Il Nuovo Cimento, vol. VI, no. 5, pp. 11–30, 1902.

G. Giorgi, “Rational units of electromagnetism,” Read before the Physical Society of London, May 27, 1902.

G. Giorgi, “Rational electromagnetic units,” Electr. World Eng., vol. 11, pp. 368–370, Sept. 6, 1902.

M. Ascoli, “On the systems of electric units,” in Proc. Transactions Int. Electrical Congr., St. Louis, MO, 1904, pp. 130–141.

F. Frezza, S. Maddio, G. Pelosi, and S. Selleri, “The Life and Work of Giovanni Giorgi: The rationalization of the units of measurement system”, IEEE Antennas and Propagation Magazine, vol. 57, no. 6, pp. 152-165, December 2015.

Supporting materials

E. Kennelly, “Adoption of the meter-kilogrammass-Second (M.K.S.) absolute system of practical units by the international electrotechnical commission (I.E.C.), Bruxelles, June 1935,” Proc. Natl. Acad. Sci. USA, vol. 21, no. 10, pp. 579–583, 1935.

Resolutions of the International Congress of Electricians, Paris, 1881.

W. Weber, “Elektrodynamische Maassbestim mungen über ein allgemeies Grundgesetz der elektrischen Wirkung,” in Abhandlungen bei Begründung der Königl. Sächs. Gesellschaft der Wissenschaften am Tage der zweihundertjährigen Geburtstagfeier Leibnizen’s herausgegeben von der Fürst, Leipzig, Germany: Jablonowskischen Gesellschaft, 1846, pp. 211–378.

W. Weber, “Elektrodynamische Maassbestim mungen, Insbesondere Widerstandsmessungen,” in Abhandlungen der Königl. Sächs. Gesellschaft der Wissenschaften, mathematisch-physiche Klasse 1, Leipzig, Germany: Jablonowskischen Gesellschaft, 1850.

W. Weber, “Messungen galvanischer leitungs widerstände nach einem absoluten masse,” Annalen der Physik, vol. 82, pp. 337–369, 1851.

P. J. Nahin, “Oliver Heaviside,” Sci. Amer., vol. 262, pp. 80–87, June 1990.

O. Heaviside, Electromagnetic Theory. London: The Electrician Printing and Publishing Co., vol. 2. 1899.


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