The fine-structure of some lines in the visible region of the spectrum of thallium III

From a study of the fine-structure of some lines in the arc spectrum of thallium Schüler and Brück concluded that the nucleus of the thallium atom possessed a moment of momentum given by ½h /2π and this value was confirmed by work on the first spark spectrum of the element. The value of the nuclear moment being known the structure of the lines in the second spark spectrum could be predicted and the present paper is the account of an investigation of a number of these lines which lie in the visible region, a comparison being drawn between the experimental and the theoretical results. The source of light used was similar to the one employed by McLennan, McLay and Crawford in the excitation of the first and second spark spectra of thallium for the purpose of line classification. It consisted of a quartz tube about 50 cm. long and 1½ cm. in diameter with a plain window in each end and provided with aluminium electrodes sealed into side tubes. The metal whose spectrum was to be studied was scattered along thé bottom of the tube and the tube evacuated. The metal was then vaporised by hear supplied by a coil of nichrome wire wound on the tube. This coil must be wound non-inductively or the desired excitation will not be obtained. The high tension across the terminals was produced by joining them in series with the secondary of a 30,000-volt transformer and a spark gap of about 1 c. m., a condenser being connected in parallel.