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on the Atmosphere of Venus. 
of the atmosphere, as far as a perpendicular height of 15000 
feet, be so dense as to reflect so clear a light upon a zone ex- 
tending 67 geogr. miles into the dark hemisphere, that we, 
at a distance of only 12 0 47' 45" from the sun, and when this 
luminary is only from 3 to 4 degrees below the horizon, can 
see it so distinctly and evidently as to be able to compare it to 
our common twilight, measuring 6° 23'^-, it must follow, that 
the atmosphere of Venus rises like ours, far above the highest 
mountains : and although we ascribe to that atmosphere the 
greatest possible transparency, it will still remain a more 
opake covering than, according to my Selenotopographical 
Observations, that of the moon appears to be. These observa- 
tions also point out the probable cause why we do not see on 
this, our nearest, primary planet, even in the most favourable 
circumstances, any of the superficial shades, which, according 
to all analogy, we have reason to suppose on this, as well as 
on all the other planetary bodies ; and which, considering the 
proximity of the planet, we should, when at its mean dis- 
tance, and with a good Herschellean telescope, magnifying 
60 or 70 times, certainly distinguish nearly as plainly as I have 
seen, even with the naked eye, the superficial shades on the 
moon, not only the greatest ones, but also some of the lesser, 
such as Copernicus, Aristarchus, &c. ; and surely, as well as 
we can discern, with a proper luminous magnifying power, 
the variable faint atmospheric stripes on Saturn and Jupiter, 
and the atmospheric opacities on Mars. At least it appears to 
me, that the density of the lower part of Venus’s atmosphere, 
which enables it to reflect so clear a light into the dark hemi- 
sphere, sufficiently warrants such a conjecture : and it may- 
well be conceived, that with so dense an atmosphere, the very 
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