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jar

1

In the British Admiralty, 19ᵗʰ century – 1937, a unit of electrical capacitance equal to the electrical capacitance of a standard 1-pint glass tankard, filled with brine and covered with tin foil, forming a Leyden jar. 1 jar = 10/9 nanofarads.

The Admiralty began phasing out the jar in 1937 (by A.F.O. 1552/37¹), using the farad instead.

William S. Harris.
Philosophical Magazine, vol 4, page 436 (1834).

1. Admiralty Handbook of Wireless Telegraphy, volume 1, Magnetism and Electricity.
London: H.M.S.O., 1938.

Page A2. See also the definition in section 168.

resources

The Leyden jar should have its capacity marked on it, expressed in fractions of a microfarad. Instrument makers still maintan the absurd custom of denominating Leyden jars as “pint size,” “quart size,” or “gallon size.” The so-called pint size has a capacity of about 1/700 microfarad, and the so-called gallon size about 1/300 microfarad.

Glass Leyden jars, as usually made, will stand charging with 20,000 volts. Hence the energy-storing capacity of the “pint size” (being equal of ½CV²) is about 0·28 of a joule at this pressure, or nearly 3/16 foot-pound. This is a very small storage compared with the over-all bulk of the jar.

J. A. Fleming.
The Principles of Electric Wave Telegraphy.
London: Longmans, Green and Co, 1906.
Page 59. We thank M. Yves Olsommer for calling our attention to this source.

2

In Ireland, an imperial pint of beer.

Terence Patrick Dolan.
A Dictionary of Hiberno-English. The Irish Use of English.
Dublin: Gill and Macmillan, 1998.

Page 148.