Jar (unit) explained

Jar
Quantity:	Capacitance
Dimension:	M^-1⋅L^-2⋅T^4⋅I^2  ^[1]

A jar was an early unit of capacitance once used by the British Royal Navy.^[2] The term originated as the capacitance of a Leyden jar. Its value is such that one farad is jars and one jar is 1111 picofarads.^[3]

History

With early spark-gap transmitters, changing the transmission frequency was most easily accomplished by changing the number of Leyden jars connected to the tank circuit. While it was possible to calculate the required capacitance directly, it was more usual to simply have a book of lookup tables which gave the number of jars needed for any likely wavelength.

Notes and References

1. Web site: eFunda: Glossary: Units: Electric Capacitance: Jar. eFunda. 22 May 2012.
2. Book: Admiralty Handbook of Wireless Telegraphy . H. M. Signal School, British Admiralty . 1931 . London . 119 .
3. Web site: English-Metric Unit Conversion Table - Electric and Magnetic . Metal Pass . 2002 . 2 September 2022 . https://web.archive.org/web/20150720223538/http://www.metalpass.com/unit/unit9.aspx . 20 July 2015 . dead.