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Last autumn Prof. Strutt observed that the vapour of boron trichloride, when admitted into the afterglow of active nitrogen, developed a band spectrum, which he photographed with a quartz spectrograph of small dispersion. It seemed likely that this result might be interest in view of certain facts already established in connection with compoubds of the chemically related elements carbon and silicon, namely, that the interaction of carbon compounds and active nitrogen developed the cyanogen bands, and that the vapour of silicon nitride. Prof. Strutt, therefore, invited me to continue tthe boron experiments with a view to tracing the origin of the new system of bands, and ddetermining the numerical relations existing in it. The remarkable scarcity of boron lines lends additional interest to any new work on the spectroscopy of boron as a possible means of detecting hitherto unrecorded lines, or of eliminating others formerly attributed to boron. In this connection Sir William Crookes was shown that the boron lines are only three in number, via., λ 3461.50, λ 2497.83, λ 2496.89 (Rowland scale), and that some lines observed by Eder and Valenta and others were due not to boron but to impurities.