General Observations regarding the Spectrum of the Aurora[17].
C. Note appearance, colour, &c. of arc, streamers, corona, and patches of light.
Get compass positions of principal features, and note any change of magnetic intensity. If corona forms, take its position and apparent height.
Look out for phosphorescence of Aurora and adjacent clouds. Listen for reported sounds. Note any peculiarity of cloud scenery, prior to or pending the Aurora.
Sketch principal features of the display, and indicate on this sketch the parts spectroscopically examined.
Examine line in red specially in reference to its assumed connexion with telluric lines (little a group), and note as to its brightening in sympathy with any of the other lines.
Examine line in yellow-green (Ångström’s) as to brightness, width, and sharpness (or nebulosity) at the edges. Notice as to a peculiar flickering in this line sometimes seen; note also whether this line is brighter (or the reverse) with a fall of temperature. Note ozone papers at the time of Aurora.
Note whether the Auroræ can by their spectra be classed into distinct types or forms, and examine for different spectra as under:—
α. The auroral glow, pure and simple.
β. The white arc.