62 Rev. C. 8. Lyman on the Auroral Bow of June, 1852. 
either at the top or bottom of the beams, and is inclined to think 
they are at the top. But if the view of the subject taken above 
is correct, the auroral bow may be regarded as nothing more than 
a curtain or sheet made up of contiguous beams, and seen more 
orlessedgewise. Such curtains, seen at such an angle as to ren- 
der their curtain-like character manifest, are occasionally noticed, — 
during an aurora, and some striking examples have been figured by 
travellers as seen in high northern latitudes, particularly at Bosse- 
kop in Finland, 1838-40, by MM. Lottin, Bravais, &c., of the Scan- 
dinavian Scientific Expedition. If we imagine such a curtain, cros 
sing the meridian nearly at right angles, and having an inclination 
equal to that of the dipping needle, to be moving slowly towards 
the south, at a height above the earth nearly equal to its vertical — 
idth, it might present successively, to a particular observer, the 
following differeut aspects. When first seen comparatively low in 
the north, and at a great distance, with other similar sheets of 
beams before or behind it in the same direction, it would help 
form the low dense arch of auroral light so often visible a few 
degrees above the northern horizon. Such a curtain, on moving 
further south, would, by the effect of perspective, appear to rise 
in altitude, and become separated from the mass of beams beyond, 
covering the northern sky with streamers more or less near to 
each other, or with a diffused auroral light. As it approached 
the zenith of the observer, the length of the beams would seem 
to shorten from being seen in perspective, while the light would 
become more condensed, and the whole assume the form of @ 
broad arch, or diffuse belt, more or Jess irregular and feathery; 
spanning the heavens. On passing to the south of the zenith, — 
its apparent width would dimiuish, and the intensity of its light 
increase, until it reached the direction of the dipping. needle, 
when being seen edgewise, its apparent breadth would be re 
duced to a minimum, and its margin become better defined. 
it passed still further south, it would again increase in width, apg 
Jiminish in brightness, until it finally vanished, or resolved itse 
into ordinary streamers. This change in the apparent width of 
the belt as it passed southwardly from the zenith, has been oftet 
noticed. [It is mentioned particularly by the observer at Edin- 
burgh, of the aurora of March, 1826, discussed by Dalton in the 
Phil. Trans. for 1828. sh 
le q 
Whether this be the true theory of the form and position of | 
. 
the belt or not, the fact that the observations before us seem 0 — 
require such a theory, should direct the attention of observers 
more particularly to the precise width of the belt, as well as 10 | 
its altitude or position among the stars. 
The numbers given above for the height of the bow of June | 
11th above the earth can be regarded only as an approximation, 
owing to the difficulty before mentioned of deciding upon the 
