A prefix used to identify electric units in the centimeter-gram-second electromagnetic system of units. It is an abbreviation for “absolute.” (The prefix “stat-” marked units in the centimeter-gram-second electrostatic system of units.)

Like the stat- prefix, the ab- prefix was more commonly used in the United States than in Europe.

graph showing the rise and fall of the abampere, abvolt and abohm between 1900 and 2000

Made with Google's n-gram viewer.



By rights, every C. G. S. electromagnetic unit should have a name. There is not even a recognized weed, or germ, that does not have a name. Practically all the fifteen hundred millions of people inhabiting the world have names. It would seem that a fundamental C. G. S. electric or magnetic unit is of as much importance as a weed or a bacillus. Moreover, it is fortunately unnecessary to learn the names for units, or commit them to memory, if the units are rarely used. It would be sufficient to have authorized names accessible and definite, ready for use when required.

Moreover, our minds are so constituted that until we possess a name for a thing, the thing remains more or less symbolical, and is not fully realized as concrete. Thereby the C. G. S. system of electromagnetic units, which is necessary and fundamental becomes hampered and retarded. It is desirable for scientific purposes, for educational purposes, and in the interests of progress, that these international C. G. S. units should have recognized names.

The expedient suggests itself of attaching the prefix ab or abs to a practical or Q. E. S. unit, in order to express the absolute or corresponding C. G. S. magnetic unit. The advantages of the plan are that it is almost self-explanatory, and requires no effort of memory to acquire; also that it is self-suggesting in all the important European languages. According to this plan

the C. G. S. magnetic unit of e.m.f. would be the abvolt
" resistance " absohm
" current " absampere
" quantity " abcoulomb
" capacity " abfarad
" inductance " abhenry or centimetre
" energy " abjoule or erg
" power " abwatt

A. E. Kennelly.
Magnetic units and other subjects that might occupy attention at the next  International Electrical Congress.
Transactions of the American Institute of Electrical Engineers, vol 20, no. 8, pg 1412 (October 1903).
A paper presented at the 20th Annual Convention of the American lnstitute of Electrical Engineers, Niagara Falls, N. Y., July 2, 1903.


Some statements in regard to units might well be qualified by the insertion of “sometimes used” or of some similar phrase; since, for example, no electrical congress has recommended the “gilbert” or the “abvolt,” objection may be taken to the statements that the C.G.S. unit of magnetic potential difference is the “gilbert” (p. 92) and the C.G.S. unit of electric potential difference is the “abvolt.”

Frederick Bedell.
Science, vol. 35 no. 904, page 662 (April 26, 1912).
In a review of Principles of Electrical Engineering by Harold Pender (1911).


Names have not been given to the cgs units of electric quantities in either the electrostatic or electromagnetic systems; names have, however, been provided for cgs units of magnetic quantities. It was suggested in 1904 by Kennelly that the cgs electromagnetic unit of an electric quantity be designated by prefixing “ab” to the name of the “practical” unit, e. g., “abohm”; and that the cgs electrostatic unit be designated by the prefix “abstat,” e. g., “abstatohm.” The suggestion has found favor with some writers, but it is more usual to write simply “cgs unit.”

[U. S.] Department of Commerce.
Circular of the Bureau of Standards No. 60.
Electric Units and Standards.
Washington: U.S.G.P.O., 1916.
Page 12.

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