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TRANSACTIONS OF THE SECTIONS. 23 
usual height above the surface of the earth is very inconsiderable in high latitudes, 
since it has been observed at one place in the zenith, forming a confused mass of 
flashes and beams; and at another, not many miles distant, having the appearance 
of a low illumined ‘arch i in the direction of the former place. 
The sudden deposition of extremely minute frozen particles, when auroral displays 
took place near to the zenith, was several times observed by the author; and it ap- 
pears that the same singular fact has been alluded to by Lieut. Hood and also by 
Dr. Richardson, but more especially by Professor Joslyn of New York, in Silliman’s 
Journal, Oct. 1838, who concludes, from numerous observations made in North Ame- 
rica, that ‘‘ the aurora is an electrical phenomenon,—that it is intimately connected 
with the elements of the clouds, and with these elements only, when they are gene- 
rated in air intensely cold, as well as nearly saturated with humidity,—that it requires 
for its development a cold adequate to the crystallization of aqueous vapours,—that 
crystals of snow, more minute and simple than those which produce halos, are 
always present in the atmosphere above the region of ordinary clouds during the 
appearance of this metedr,—that those seasons of the year, and those hours of the 
night when the aurora most frequently occurs, are favourable both to the presence 
and congelation of aqueous vapours in the atmosphere.”’ The author remarks upon 
the singular agreement between these results of Professor Joslyn and those commu- 
nicated by himself four years before, in an unpublished paper to the Royal Society. 
He considers, however, that perhaps the strongest proof of the important agency of 
these particles in an auroral display, is to be derived from the fact, that the auroral 
light can be distinctly traced to those localities where humid vapours are known to 
be undergoing rapid congelation, and where such particles must in consequence 
abound; and that in the usual arch- formation, whatever may be the nature of the 
light, yet the auroral fringe clearly arises from the illumination of the frozen parti- 
cles which are formed from the exterior portion of the vapours, being under the in- 
fluence of the cold atmosphere immediately above them. From the circumstance 
that congelation is a known source of electrical development, he infers that strong 
evidence is thereby afforded of the nature as well as the locality of the aurora. 
Although he considers sufficient evidence was obtained as to the direction and 
situation of the open-water during the winter season, from the usual indications of 
the sea-blink, and also from the information obtained from the Esquimaux, yet a 
singular confirmation in this respect was afforded by the circumstance, that the re- 
fraction due to the star Sirius, which was usually observed through a low aurora in 
the south-east direction at the island of Igloolik during the second winter, was ge- 
nerally about 1' less than the corresponding refraction of the same star when ob- 
served at equal altitudes and temperature towards the south-west ; in which latter 
direction the visual ray passed over land covered with ice and snow, thereby indi- 
cating a diminished density of the lower stratum of atmosphere in the former direc- 
tion, in which the aurora was seen, from its being under the influence of the compa- 
ratively higher temperature of an exposed surface of the sea. 
The author remarks, that when a display of aurora commenced with the arch- 
formation, the upper stratum of vapour, which formed the exterior limit or upper 
edge of the arch, was usually of a very dense and dark appearance, apparently highly 
charged with humidity, and exhibited by the contrast the auroral fringe immediately 
above it with splendid effect ; but that the lower portion, being of a higher temperature, 
from being nearer to the exposed surface of the water, became frequently so dilated 
and transparent as to render stars visible within the arch. 
To form an estimate of the prodigious extent to which congelation goes on during 
the winter season near the margin of the frozen sea, and at those places within it, 
where, by reason of the spring tides, the ice is continually broken and separated 
from the land, and the water in consequence suddenly exposed to the action of the 
low temperatures which then prevail, he observes, that a difference of more than 
70° Fahr. continually occurs between the temperature of the exposed surface-water 
and that of the atmosphere above it, and that the latter in consequence becomes im- 
mediately impregnated with extremely minute frozen particles, known by the name 
of “ Frost-smoke,” which, when seen at a distance, has a white silvery appear- 
ance. 
_ The immense mass of vapours which are known to accumulate near the edge of 
