A jar was an early unit of capacitance once used by the Royal Navy.[1] The term relates to the capacitance of a Leyden jar.
Its value was defined such that 1 microFarad = 900 jars.
Or, 1 jar = 1.111... nanoFarads.
With early Rotary Spark Transmitters changing the transmission frequency was most easily accomplished by changing the number of Leyden Jars connected to the oscillatory 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.
References
- ^ Admiralty Handbook of Wireless Telegraphy, 1931, p.119. HMSO, London.
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