THE AURORA. 63 
‘altitude of the vertex will be more difficult to determine, owing to 
its variability, but, when possible, the altitude and the azimuth of 
the points where the arch rests on the horizon should be simul- 
taneously observed. If the observations are always made from the 
same spot it may be possible to place landmarks so that azimuth 
and altitude may be quickly determined. The important questions 
as to the relation of the aurora to cloud formations, and of their 
periodicity, can only be satisfactorily dealt with if a careful record is 
kept of every appearance of the aurora. 
The observers cannot do better than to follow the guidance of the 
system of observation adopted by the Austrian Expedition during 
the international polar observations carried out at Jan Mayen, and 
published by the Austrian Academy of Science. The appearance of 
the aurora, following Weyprecht’s guidance, is there divided into 
eight features. 
1. The Arch.—The inside of the arch is often described as being 
very dark, and stars are observed in it. Such cases should be recorded. 
2. Bands,.—These make the impression of being portions of arches, 
changed in form and direction, and often moving about irregularly. 
3. Filaments and Streamers—The expression filaments may be 
taken as the equivalent of the German “Faden,” while the German 
word Strahlen is applied by the Austrian Expedition to what we 
should call “streamers.” Filaments and streamers differ chiefly by 
their width, which is narrow and uniform in the case of filaments, 
while streamers are wide and tapering at one end. The direction 
and motion of these streamers is of importance. When they are 
parallel and nearly vertical they give the idea of “draperies” or 
“curtains,” and the appearance is sometimes described in this way. 
4, The Corona.—This appears always near the zenith, and is a very 
characteristic phenomenon. A circular band is formed round the 
zenith, either by the apparent contraction of an arch or by sym- 
metrical arrangements of bands, filaments or flames. Streamers 
or filaments shoot out from the corona towards the horizon. 
5. Auroral Nebulositics.—These are indistinct nebulous masses, 
floating about without distinct outline. 
6. Auroral Segments.—This is described by Weyprecht as “an 
apparently dark segment of a circle, which is bordered by a low- 
lying, not varying, luminous arch, and is situated in the magnetic 
North and South. These segments have not been seen at Jan Mayen. 
7. Auroral Glow.—A luminous appearance, high up in the sky, 
the filaments diverging towards the zenith. 
8. Fans and Flames.—These are luminous appearances to which 
