A pair of highly-sensitive, Leeds and Northrup, Model 2239 galvanometers. These devices, which measure 15 cm in width and 24 cm in height, were used to measure extremely small currents during the 1940s and 1950s before the development of sensitive electronic meters. A small current through the device produced a deflection of the mirror attached to a coil placed within a magnet. The degree of deflection was related to the current. One of these devices, labeled 2239-F, appears well used while the other, (2239-B), appears to have its original packing for shipping. These devices were used by the Nuclear Physics Branch at Chalk River.