The unit of magnetic flux density in the centimeter-gram-second electromagnetic system of units, but see below. Symbol, Gs, sometimes G, especially as milligauss, mG. One gauss is a magnetic flux density of 1 maxwell per square centimeter. One gauss corresponds to 10−4 tesla in SI, although strictly speaking the two units cannot be compared. Usually encountered as milligauss. Sometimes called the abtesla; symbol, abT.
Painted copy by G. Biermann of a portrait by C. A. Jensen (1792-1870) painted in July 1840
The gauss is named for the German mathematician Karl Friedrich Gauss (1777–1855).
The late 19th and early 20th centuries saw more confusion over the meaning of “gauss” than practically any other scientific unit. This confusion arose from the way the cgs electromagnetic system was constructed, having been based on unit magnetic poles. To serve as the phantom fourth dimension that the system needed to be able to include electric and magnetic units, the permeability of free space was set equal to 1 and considered merely a numeric ratio, not a physical quantity. The result was that in the cgs electromagnetic system of units, in free space magnetic field strength (whose conventional symbol is H) and magnetic flux density (symbol, B) are numerically equivalent. The dimensional identity of measures of B and H in the cgs electromagnetic system created the illusion among some workers that B and H were the same. They are, however, different. By analogy, if H is the force that compresses a spring, B is the extent of the compression. Some used the gauss to measure both,1 some used it only for H and some only for B. These preferences were often national. In the United States after 1900, for example, the gauss was used for B and the gilbert per centimeter for H.
To add to the confusion, in 1895 the British Assn. Committee on Electrical Standards tentatively recommended that the cgs unit of magnetomotive force be called the gauss.
Further, it is said that those researching the earth’s magnetic field used the gauss as the cgs unit of H, but experts dispute this.2
In 1900, after heated discussion the Fifth International Electrical Congress adopted the name Gauss for the C.G.S. unit of magnetic field (see the report in Nature). It was noted in the discussion that in the United States the “gauss” had been a unit of magnetic field “for some years.”
At its meeting in Stockholm in 1930 the Advisory Committee on Nomenclature of the International Electrotechnical Commission eliminated all ambiguity by adopting the gauss for the unit of magnetic flux density and the oersted for the unit of magnetic field strength.3 (The term oersted had previously been used for the unit of magnetic circuit reluctance.4)
According to the current national standard in the United States5, the gauss is not to be used; the tesla should be used instead. In practice, however, in the early 21st century the gauss remains the preferred unit in many fields, from astrophysics to magnetic recording technology.
1. American Society for Testing Materials.
Yearbook 1915.
Page 195.
American Institute of Electrical Engineers, Standardization Rules, Rule No. 90; 1915. (provisional)
2.
J. H. Dellinger.
International System of Electric and Magnetic Units.
Bulletin of the [U.S.] Bureau of Standards, volume 13,
number 4 (March 6, 1917).
See footnote 8 on page 612.
3. International Electrotechnical Commission.
Recommendations in the field of quantities and units used in electricity. (1st ed.)
IEC Publication 164.
Geneva, 1964.
Page 27.
4. The name was suggested by the Committee of Units and Standards of the American Institute of Electrical Engineers in May 1900.
5. IEEE/ASTM SI 10™-2002.
American National Standard for Use of the International System of Units (SI): The Modern Metric System.
New York: IEEE, 30 December 2002.
See Section 3.3.3.
A unity [sic] of intensity of magnetic field, proposed by Prof. S. P. Thompson. = 108 C.G.S. units. Other values have been suggested.
Latimer Clark.
A Dictionary of Metric and Other Useful Measures.
London: E & F.N. Spon, 1891.
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