af Soe Trans. Acad. Sci. of St. Louis 
EXPLANATION OF PLATES. 
Fig. 1. The aurora when first seen at 7:30 p. m., showing the 
arch which contrasts sharply with the very dark area below. The 
hilltops can be seen still illuminated by the twilight. 
Fig. 2. Between 9:18 and 9:40 p. m. The sky is now darker 
and the arch brighter; six rays are shown extending from the arch 
to the horizon. 
Fig. 3. 9:40 p.m. The first few rays that appeared are shown 
extending upward from the widened arch. 
Fig. 4. 10:15 p.m. The dark area beneath the arch has become 
as bright as the arch and merged with it. More rays are shown, 
including the great ray near the western end of the arch. 
Fig. 5. 10:38 p.m. The display at the time of maximum ac- 
tivity. Many of the great rays are seen, but it is entirely impossible 
for a drawing to give an adequate impression of the rapid move- 
ment produced by the darting and playing of the rays. 
Fig. 6. 11:47 p.m. The dark seat beneath the arch has 
reappeared. Many small cloud-like areas are shown, while the 
dark waves parallel with the horizon are moving upward across 
em. e upper extremities of a few rays can be seen above the 
TE—The principal features of the aurora were sketched on 
the morning after observation, from notes made during its progress. 
sey drawings for the plates were made from these sketches after- 
ard. 
