12 ON THE RECENT SECULAR PERIOD 



period. Dr. Gibbons, like Professor Joslin, took particular note of the state of the 

 thermometer, and infers that the occurrence of an aurora is always attended and 

 followed by a depression of temperature. He shows that the average temperature 

 of the days immediately preceding the auroras was 55°; that of the daj's following 

 52° ; and that the difference between the second days before and after the auroras" 

 was G°. 



In 1836 the number of the exhibitions of the aurora borealis greatly increased; 

 being, as given in the Regents' Report, no less than sixty-one. The month of April 

 was remarkably productive, the aurora being seen on the 8th, 11th, 12th, 19th, 

 20th, 21st, 22d, 23d, and 24th. That of the 22d was of the first class, and the 

 description of it, written by the author of this paper at the time, was as follows : — 



" Soon after 7 o'clock, near the end of twilight, a thick covering of auroral vapor 

 was seen to overspread the northern hemisphere, and streamers began to shoot up 

 towards the zenith, accompanied by faint undulations, all tending towards the pole 

 of the dipping needle as a common focus. At this period, the color of the aurora 

 was a dull yellow, with a slight tinge of red ; but, as the exhibition advanced, the 

 red predominated. The aurora made slow progress, but the firmament was surpass- 

 ingly beautiful, particularly in the west, where the planet Venus, now approaching 

 its maximum splendor, the planet Jupiter, and the Moon, near its first quarter, 

 appeared one above the other along the zodiac, while the large constellation Orion, 

 with Sirius and Procyon in his train, conspired to adorn the western sky. Saturn 

 also was shining brightly in the southeast. About half past 10 o'clock began the 

 auroral waves (which were very remarkable on that night), and increased rapidly 

 until 11 o'clock; after which they continued, with surprising activity, nearly all 

 night, ascending with swift undulatidns towards the magnetic focus, traversing 

 about half the quadrantal arc in half a second of time. At five minutes after 11, 

 a number of broad stripes of silvery whiteness appeared in the east and west, all 

 tending upwards to the same point. These were soon replaced by sheets of crimson 

 eight or ten degrees broad below, but tapering above. They crossed the constella- 

 tion Leo in the west. They had a counterpart in the east, though somewhat less 

 splendid. Soon afterwards broad sheets wreathing themselves in serpentine curves, 

 flowed towards the magnetic pole, with astonishing rapidity, on every side, but 

 most abundantly from the N. W. and the N. E. Their margins were fringed with 

 a white light of peculiar softness. They were like crimson billows, separated by 

 horizontal lines, and rolling towards the zenith. During the fifteen minutes, while 

 these crimson sheets were in view, two parallel arches stretched across the southern 

 sky, the lower about 30° in altitude, from both of which streamers arose. From 

 half past eleven o'clock, the auroral waves exceeded everything as they rushed in 

 pallid, filmy sheets towards the zenith, along the line of the streamers, though 

 apparently much below them, increasing their velocity as they ascended. 



" The focus changed its position slightly at different times-; first moving northwards, 

 and then returning. At 12 o'clock it had a declination of 23 i degrees, and a right 

 ascension of 209 degrees. The barometer remained through the night nearly 

 stationary, and the thermometer fell only 2° after midnight : namely, from 32° to 

 30°. At half past 2 o'clock clouds (cirro-stratus) came up, and were scattered over 



