Mercury Band System in the Neighbourhood of the Resonance Line.

A BAND in the mercury spectrum referred to as 2540 has been the subject of much discussion, owing to its proximity and apparent relationship to the resonance line 2536.52, and to the fact that it is seen in absorption by unexcited mercury vapour of suitable density. I have long suspected that this is only one feature of a complicated band system in this neighbourhood. The investigation is much embarrassed by the glare of the resonance line, which makes it difficult to photograph delicate details in the immediate vicinity.