It is argued that precision measurements which rely on the use of conductive housings for electrical screening may well be subject to spurious error owing to charge induction within the housing. If the momentum transfer processes associated with the absorption of thermal radiation act selectively upon electrons, a residual charge may be induced on surfaces internal to the housing and held in place by radiation pressure. The effects of such action upon the measurement of G is discussed in relation to anomalies reported in such measurements. The phenomenon is supported by the existence of the charge on the Earth's surface. A method of testing for the presence of induced charge and eliminating its effects is indicated. © 1982.