A device for influencing an electron beam, for example a beam deflecting device in an electron beam lithography machine, comprises a beam influencing coil (13) operable to influence an electron beam (EB) in the vicinity of the device by way of a magnetic field and a heat dissipation compensating coil (14) operable to provide a heat output so compensating for any change in heat dissipation of the device due to operation of the beam influencing coil (13)—particularly variable operation to vary the field intensity or to create and remove a field—as to reduce the amount of change, preferably to maintain the net heat dissipation at a constant value. The compensating coil (13) can be controlled, for example, by measurement (19) of the heat dissipation of the device and calculating (18) current supply (16) to the coil (13) in dependence on the measured dissipation.