lamp. Furthermore, the greater currents produce an increased number of unexcited atoms in the cloud. The unexcited atoms, in tum, are capable of absorbing the radiation emitted by the excited ones. This self-absorption leads to lowered intensities, particularly at the center of the emission band. A variety of hollow cathode lamps are available commercially. The cathodes of some consist of a mixture of several metals; such lamps permit the determination of more than a single element.