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POPULAR SCIENCE REVIEW. 
if not quite as large as the Moon, though in other respects hearing no 
resemblance to that body, being of a hazy contour, emitting a dazzling 
blue light at first, which became afterwards of a yellowish tint. Although 
visible for only a few seconds, no person in the open air at the time could fail 
to notice it as it came out of the sky with the quickness of a flash of light- 
ning, and disappeared equally suddenly, its course being in the direction 
from Mars to the Moon. We hope in our next to be able to give some 
account of its track and height. 
The Comptes Rendus, November 17, contain a letter from P. Secchi to 
M. Elie de Beaumont, concerning the planet Mars, in winch the former 
states, that there can be no doubt that the white polar blotches on that 
planet are masses of snow, or of clouds condensed at the poles ; that the 
persistence of the blue channels show them to be seas, and the red patches 
continents. 
The comet first discovered by M. Bruhns will be visible in those, 
latitudes during the month of January. On January 1, 1803, it will be 
close to the star Kappa Coronse (of mag.), and not far distant from 
the star Zeta (of 4th mag.). It travels after this to the constellation of 
Vulpecula, and is close to Flamsteed 25 on January 28 (of Gth mag.). It 
is at its greatest brilliancy on January 1. 
The second comet has disappeared at present, but may probably be 
visible at the end of February. It likewise is at its greatest brilliancy on 
January 1. On February 17, it is in the constellation of Cetus. 
BOTANY. 
Artificial Formation of Cork. — M. Casimir de Candolle, the third of 
that name, describes the mode by which, in Algeria, superior cork is 
obtained from the cork oak. The rough corky layer is removed down 
to the subjacent cellular envelope, or green layer, during summer and 
autumn. In consequence of this removal a new corky stratum forms upon 
the green layer at a variable distance from its denuded surface. This 
stratum grows in annual layers upon its internal surface, just as the 
original worthless corky layer did ; but it is much finer, and more elastic. 
After seven or eight years it is sufficiently grown to be removed, and the 
same process is repeated. This may be done many times, and new cork 
removed every seven years to an almost indefinite extent. 
The Exhalation of Ozone by Plants. — In the Comptes Rendus, M. Kosman 
details experiments from which he deduces these results : That plants dis- 
engage ozonised oxygen from their green parts, during the day, in greater 
ponderable quantity than exists in air. During the night the same thing 
takes place, if accumulated masses of vegetation are in vigorous growth. 
Town plants disengage less ozone during the day than country plants ; 
hence the air of the country is more mvifiant. In the midst of the town 
there is more ozone in the air at night than during the day. The corollas, 
or coloured parts of the flower, do not disengage ozonised oxygen ; and, 
lastly, in inhabited rooms, oxygen does not generally exist in an ozonised 
state. 
