In the course of Prof. Fowler’s recent observations of the principal series of hydrogen lines in the spectra of helium tubes traces were frequently seen of a band spectrum the origin of which was unknown, and of which no previous record could be found. The most prominent features visually were bands having their heads at about λλ 6400, 5732, 4649, and 4626. The band at 5732 was degraded towards the violet end of the spectrum, the opposite being the case with the other three. Although in the first instance the new bands were always comparatively feeble, they were such a frequent and persistent feature of the spectra of the various tubes that it was thought desirable to investigate their origin, and to determine their positions. It was soon found possible, by choosing suitable conditions of pressure and discharge, to obtain the new spectrum quite brightly, when a number of other bands were observed, some visually and others by photography. These bands were evidently associated with those first noticed.