Abstract: A linear actuator comprising of two elongate resilient elements (10, 12) joined together at their opposite ends (13, 14), a first one of the elements is fixed at a point intermediate its ends (16) and the two elements (10, 12) are arranged to carry an electric current which causes the two elements (10, 12) to move apart when they are placed in a transverse magnetic field. The linear actuator may be used to control the opening and closing of a valve in a fluid dispensing device, where a needle (20) is attached to the second element (12), which needle co-operates with a valve orifice.

Abstract: An instrument for counting the number of elements in a stack is moved over the side of the stack and an image of a portion (S) of the stack is formed on a linear photocell array(16). The photocell array is continually scanned and its electrical scan output signal is fed to a correlator which carries out an auto-correlation function while the instrument is initially stationary, and then a cross-correlation function as the instrument is moved, to furnish a time varying signal having a characteristic periodicity representing successive elements in the stack. The repeating cycles in this signal are counted to provide a count of the number of elements in the stack.