In the United States, a unit for reciprocal farads (farad spelled backwards!). Symbol, F⁻¹. Used to measure elastance, the reciprocal of capacitance. Proposed by Vladimir Karapetoff in 1910. A. E. Kennelly but not much used.¹

1. A. E. Kennelly.
Journal of the Institute of Electrical Engineers (GB) volume 78, page 241 (1936).



Elastance of dielectrics could be properly measured in units called darafs, one daraf being the reciprocal of one farad; it is therefore designated by the same name spelled backwards (same as ohm and mho). As the farad is too large a unit, so the daraf is too small a unit for practical purposes; elastances are conveniently measured in megadarafs, same as insulation resistance is measured in megohms. One megadaraf is the reciprocal of one microfarad. There is little doubt that with the extended use of extra-high voltages there will be more and more need for electrostatic calculations, and for a scientific design of insulation; then some such names and units will have to be agreed upon.

V. Karapetoff.
The Electric Circuit.
Ithaca [NY]: [no publisher] 1910.
Page 72. An 85-page pamphlet prepared for his students.


Discussion on "Pre-Charged Condensers in Series and in Parallel" (Karapetoff), Atlantic City, N. J., June 28, 1918.

V. Karapetoff: Regarding my nomenclature, I do not like the word daraf, but I wanted to create a disturbance among our rigorists in order to induce the Committee on Nomenclature to take some action. To make the situation particularly objectionable, I also spelled the word henry backward, making it yrneh, which word is used in my "Magnetic Circuit". It is not for an individual to coin a new word, and I felt that I was more consistent in following the established practise (ohm, mho) than in inventing a new word. I will be the first one to adopt a new word for reluctance, the reciprocal of henry, and for the daraf, the reciprocal for farad, as soon as an international action has been taken.

Transactions of the American Institute of Electrical Engineers, vol. 37, pt. 2 (July-December 1918)
New York: American Institute of Electrical Engineers, 1918.
Page 1025.


DARAF.—A name proposed by Prof. V. Karapetoff for the unit of elastance. Since the latter was proposed as the reciprocal of capacitance, the daraf would be the reciprocal of the farad, its unit. Daraf is farad spelled backward.

Frank H. Bernhard, editor.
EMF Electrical Year Book.
Chicago: Electrical Trade Publishing Company, 1921.
Page 212.


By the elastance S of a condenser is meant the reciprocal of its permittance. The elastance is therefore the ratio of the potential difference to the charge in the condenser. The unit of elastance is termed the daraf. A condenser with a permittance of one farad has an elastance of one daraf.

Edward Bennett/
A Digest of the Relations between the electrical Units, and of the Laws Underlying the Units.
Bulletin of the University of Wisconsin No. 880, Engineering Series vol 8, no. 6, pages 333-426.
Madison: University of Wisconsin Engineering Experiment Station, Nov. 1917.
Page 27.


It will probably be of advantage in training future students of alternating-current electricity to stress more than in the past the presentation of the ideas concerning elastance contained in this paper. Professor Karapetoff¹² has shown the usefulness of the idea of elastance when condensers are joined in series and has called attention to the hydraulic analog of the electrostatic circuit. He has called the reciprocal of the farad the “daraf.” Professor Kennelly¹³ has also found the idea of elastance useful. But neither of these writers mentions the idea of mutual elastance.

Cordial acknowledgment is made of helpful suggestions received in the preparation of this paper from Dr. A. W. Smith of this laboratory and from Dr. J. H. Dellinger of the Bureau of Standards.

12. The Electric Circuit, Chapters 6 and 7.,

13. Proc. Inst. Radio Eng. 4, 1916, p. 47.

F. C. Blake.
On Electrostatic Transformers and Coupling Coefficients.
Journal of the American Institute of Electrical Engineers, vol 40, no. 1 (Jan 1921).
Page 29.

The acknowledgment of Dellinger's support is significant, as the U.S. Bureau of Standards took up the cause of the daraf.


Glazebrook etc 1933

The Europeans, however, were not interested.


Fortunately the reciprocal has not been introduced, and we have not been threatened with "daraf" as the name of a unit.

G. W. O. Howe.
Scottish Centre: Chairman's address. The Nomenclature of the fundamental concepts of electrical engineering.
Journal of the Institution of Electrical Engineers, vol 70 issue 420, pages 54-61 (December 1931).

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