on the Atmosphere of Venus. 315 
setting shines from the horizon, is but feebly illuminated ; so 
also is Venus circumstanced with regard to the light it receives 
from the sun. To compare with some accuracy the intensity 
of light at the terminating borders on our earth, relatively to 
its full perpendicular illumination, with the same phaenomenon 
on Venus, may, for want of opportunities to observe both 
planets at once from a proper distance, as may be done with 
regard to Venus and the moon, not be very feasible ; but this, 
I think, I may with great confidence infer from my long series 
of observations, that Venus has an atmosphere in some respects 
similar to that of our earth, and which must far exceed that of 
the moon in its density, or power to weaken the rays of the 
sun. 
Thus far had I proceeded in my observations, when the 
heavens favoured me with the following ones, which may 
prove the more interesting, as they not only confirm those 
hitherto made, but also lead to some farther inferences con- 
cerning the atmosphere of Venus. 
Among all the favourable circumstances for observing the 
planet Venus, none could be more so than those I had in the 
months of March and April, but especially from the pth to 
the 16th of March, 1790, when, besides the almost constant 
and unusual serenity of the sky, the planet, which w ; as then 
in Aries, at 7 0 and 8° N. declination, was so high above the 
horizon, that, notwithstanding its approaching inferior con- 
junction on the 18th of March, at 4 P. M. I could still view it 
on the 16th, and should certainly have observed it during the 
conjunction, had not the weather become hazy on the 17th. 
Under these very fortunate circumstances, I fell accidentally 
(not having, after ten years of constant attention to Venus, 
