. Narrative of a journey to the shores of the Polar Sea, in the years 1819, 20, 21, and 22 [microform]. Scientific expeditions; Expéditions scientifiques. No. III.] LIEUTENANT HOOD ON THE AURORA. 5S1 they separate into parts. Those arches, which were bright at the horizon, in- crease their brilliancy in the zenith, and discover the beams of which they are composed when the interior motion is rapid. This interior motion is a sud- den glow, not proceeding from any visible concentration of matter, but burst- ing out in several parts of the arch, as if an ignition of combustible matter had taken p
. Narrative of a journey to the shores of the Polar Sea, in the years 1819, 20, 21, and 22 [microform]. Scientific expeditions; Expéditions scientifiques. No. III.] LIEUTENANT HOOD ON THE AURORA. 5S1 they separate into parts. Those arches, which were bright at the horizon, in- crease their brilliancy in the zenith, and discover the beams of which they are composed when the interior motion is rapid. This interior motion is a sud- den glow, not proceeding from any visible concentration of matter, but burst- ing out in several parts of the arch, as if an ignition of combustible matter had taken place, and spreading itself rapidly towards each extremity. In this motion the beams are formed, such as are described in t)ie last observations upon the subject. They have two motions, one at right angles to their length or sideways; and the other, a tremulous and short vibration, in which they do not exactly preserve their parallelism to each other. By the first, they pro- ject themselves into wreaths, serpentine forms, or irregular broken curves. The wreaths, when in the zenith, present the appearance of Coronse Boreales. The second motion is always accompanied with colours ; for it must be ob- served, chat beams are often formed without any exhibition of colours ; and I have not, in that case, perceived the vibratory motion. The beams, in differ- ent Aurorse- and sometimes in the same, are of different magnitudes, arising, probably, liom their various distances. These evolutions, often repeated, destroy the shape and coherence of the several arches ; though they, doubtless, retain the arched appearance to the eye of a spectator at the southern horizon. For it would be absurd to suppose, that these changes occur only in the zenith of one particular place. The observations, at different places, in 1820, afford satisfactory proof to the contrary. And the numbet of arches often increased or diminished, in their advance to the zenith, by a dismemberment of which, from their dist
Size: 1564px × 1598px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, booksubjectscientificexpeditions, bookyear1823
