On the constitution of the mercury green line λ = 5461 Å. U., and on the magnetic resolution its satellites by an echelon grating

In a previous communication on the series lines in the arc spectrum of mercury, attention was drawn by the writer to the excellence of the spectrograms obtained when a highly exhausted commercial Cooper Hewitt mercury arc-lamp was used as the source of the light. With this lamp, provided with a side tube carrying a window of thin crystalline quartz, it was found that exceedingly good definition was obtained over the whole range of the spectrum from slightly beyond λ = 7000 down to λ = 2150. When using the lamp at a later period in making some observations with an echelon grating of high resolving power on the structure of some of the finest lines in the visible portion of the spectrum, it was found that the components of a number of these lines also came out with exceedingly good definition.