Image: Leyden unit jar

Description: Drawing of a 'Harris jar' or 'unit jar', a small Leyden jar invented by British scientist William Snow Harris and used for measuring electric charge, attached to an electrostatic machine, from mid 1800s. Alterations: removed caption, and noise in white spaces. In operation, the top terminal (b) is attached to a load. The large bottom electrode is constantly being charged by the electrostatic machine, and the charge builds up on the Leyden jar (K). When the voltage reaches the breakdown voltage of the adjustable spark gap (n,n') it sparks over and discharges the Leyden jar into the load. Then the jar charges up again and the process repeats. Since the same amount of charge is transferred with each spark, the total amount of charge going to the load can be found by counting the sparks.
Title: Leyden unit jar
Credit: Downloaded from Henry Minchin Noad (1868) The Student's Text-book of Electricity, Lockwood & Co., London, p.57, fig.55 on Google Books
Author: Henry Minchin Noad
Permission: Public domain - author died in 1877
Usage Terms: Public domain
License: Public domain
Attribution Required?: No