35 2 Mr. Schroeteii’s Observations 
also for the several obscurations and returning serenity, the 
eruptions, and other changes I have frequently observed in the 
lunar atmosphere. This observation also implies, 
2. That the atmosphere of the moon is, notwithstanding 
this considerable density, much rarer than that of our earth. 
And this, indeed, is sufficiently confirmed by all our other lu- 
nar observations. I think I may assert, with the greatest con- 
fidence, that the clearer part of our twilight, when the sun is 
4° below our horizon, and when we can conveniently read and 
write by the light we receive from it, surpasses considerably 
in intensity the light which the almost wholly illuminated disk 
of our earth reflects upon the dark hemisphere of the moon 2^ 
days before and after the new moon. But should we even ad- 
mit an equal degree of intensity, it will, however, appear 
from computation that our inferior atmosphere, which re- 
flects as strong a light over 4 0 as that of the moon does over 
2 0 34' of their respective circumferences, must be at least eight 
times higher than that of the moon. 
3. The striking diminution of light I noticed, in my twelve 
years observations on Venus, likewise indicates that the atmo- 
sphere of that planet, which is in many respects similar to 
ours, is much denser than that of the moon ; and this will be 
still farther corroborated, if we compare together the several 
measurements and computations made concerning the twi- 
lights of different planets. There is no doubt but that the 
faintest twilight of Venus, as seen either before or after the 
rising and setting of the sun across our twilight, is much 
brighter than that of the moon ; and it appears, moreover, 
from computation, that the denser part of the atmosphere of 
Venus measures at least 13000 Paris feet in height, and spreads 
