The "radiant" spectrum

Abstract

The title refers to an interesting optical effect observed and described many years ago by Sir David Brewster (Phil. Mag., September, 1867), which appears, however, never to have been satisfactorily explained. When a small brilliant source of light is viewed through a prism held in front of the eye, a remarkable appearance is noticed, represented roughly in the accompanying diagram (Fig. 1). In the continuation of the spectrum of the source, but considerably beyond its violet end, is seen a patch of light consisting of streamers radiating from a centre, as shown. A brief statement on the cause of this effect, as determined in an investigation made by me, may be of interest to readers of Nature.