Abstract
The Paper gives an account of experimental work which has led to an extension of our knowledge of the second spark spectra of In and Ga, into the region of long wave-lengths. After making a careful study of the spark spectra of the elements in hydrogen and air under different conditions of excitation the author has identified the lines corresponding to the second series in the spectra of doubly-ionised Indium and Gallium. The principal features of the spark spectra are now known, and all these structures are in beautiful accord with the quantum theory of spectral line emission.

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