The wave lengths corresponding to more than 1,500 lines photographed in the arc and spark spectra of lanthanum were measured relative to standards in the iron spectrum. The values extend from 2,142.81 A in the ultra-violet to 10,954.6 A in the infra-red. Data on the furnace spectra of 695 lanthanum lines studied by King and Carter in the interval 2,798 to 8,346 A are quoted. Measurements of Zeeman effects for 476 lines ranging in wave length from 2,791 to 7,483 A are also presented. Comparison of relative intensities and other characteristics of lines in the different sources permitted a sharp discrimination between three classes of lines; about 700 are ascribed to neutral atoms (constituting the La i spectrum), 800 originate with singly ionized atoms (La n spectrum), and 10 belong to doubly ionized atoms (La in spectrum). These data form a complete and accurate description of atomic lanthanum spectra, suitable for chemical indentification and for analysis of the spectral structures. A new infra-red sequence of La O bands is appended.
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William F. Meggers (1932) studied this question.