SI, the international system of units
Tóm tắt
Two types of systems of units have been formed. The commercial is a system of weights and measures, such as the metric, defined by civil law. The scientific is a system of physical units generated through use of scientific laws which link corresponding quantities. The International System of units, denoted SI, was established in 1960 by the General Conference of Weights and Measures. The set of SI units included therein is the only comprehensive, coherent system of physical units. There is only one SI unit, whose value is unambiguous, for each physical quantity. Included in the SI, but not in any CGS system, are the volt, ampere, ohm, and watt, which are the only units used for measurement of the corresponding electrical quantities. Also included in the SI are prefixes used to form non-coherent, decimal multiples and sub-multiples of SI units. A few other units, such as the day, degree of arc, and degree Celsius may be used with SI units. Precepts for use of the SI, conversion tables, and geophysical constants expressed in SI units are given.
Tài liệu tham khảo
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A. E. Kennelly provides a history of electrical and magnetic units up to 1935, inJ. Instn. Elect. Eng. 78, 235, 1936.
BA: 1874,Report of the 43rd Meeting, 1873,43, 222.
Chapman, S. and Bartels, J.: 1940,Geomagnetism 2, 928, Oxford University Press, London.
Clark, Latimer and Bright, Sir Charles: 1862,BA Report for 1861,31, 37. Only a brief summary of their article is given. The complete article could not be located; it may not have been published.
Gauss, Carl Friedrich: 1877,Werke 5, 79–118. This article in his collected works was published in Latin in 1841, in Vol. 8 of theCommentationes of the Royal Scientific Society of Göttingen. A summary in German was published, apparently, in 1833. It is reprinted also inWerke 5, 293–304.
Giorgi, Giovanni: 1901,Atti dell' Assoc. Elettre. Ital. 5, 402.
IEC: 1964,Recommendations in the Field of Quantities and Units Used in Electricity, Pub. 164, Geneva.
Jenkin, Fleeming (ed.): 1873,Reports of the Committee on Electrical Standards, 1862 to 1869. The collectedReports in this volume had been revised by Lord Kelvin, Joule, Maxwell, and Jenkin. Terms such as ‘volt’ and ‘ohm’ appear in the revised 1863Report, but not in the original.
Maxwell, James Clerk: 1873,A Treatise on Electricity and Magnetism. Maxwell revised the first 9 chapters of the 2nd edition; he died in 1879. Later editions and editors were: 2nd, 1881, W. D. Nivens, and 3rd, 1891, J. J. Thomson. I have used a reprint of the 1891 edition.
Page, Chester H.: 1970,Am. J. Phys. 38, 421.
Page, Chester H. and Vigoureux, Paul: 1970. The English translation was published under the titleThe International System of Units by Her Majesty's Stationery Office, London, 1970, and by the U.S. National Bureau of Standards, Special Pub. 330, U.S. Govt. Printing Office, Washington, D.C., 1971. Second edition Special Publ. 330, 1972.
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Stacey, Frank D.: 1969,Physics of the Earth, John Wiley & Sons, Inc., New York. Tabular material was used with permission of the author and publisher.
Terrien, J. and de Boer, J.: 1970,Le Système International d'Unités, OFFILIB, 48 rue Gay-Lussac, F75-Paris 5e. Second edition, 1973.
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Thomson, William: 1851,Phil. Mag., Ser. 4,2, 551. He derives the emf of a cell in absolute units from thermodynamical considerations.
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