Faraday's voltameter. This is a device invented by Michael Faraday (1791-1867) that is used to measure a quantity of electrical charge. This version, made in 1832, was originally called a 'volta-electrometer'. A silver nitrate solution is placed in the v-shaped tube, covering the two silver electrodes. A current is passed for a known amount of time. The electrodes are weighed before and after the experiment - the amount of silver deposited at the cathode is directly proportional to the total charge that has passed. This object is preserved at the Royal Institution, London.