2l8 
Dr. Herschei/s Observations 
with micrometers adjusted to the utmost degree of precision 
in order to decide with perfect confidence that she is, as ap- 
pears most likely, larger than the earth. 
The remarkable phaenomenon of the bright margin of Ve- 
nus, I find, has not been noticed by the author we have re- 
ferred to : on the contrary, it is said, page 310, “ this light 
appears strongest at the outward limb ab c, from whence it de- 
creases gradually, and in a regular progression, towards the in- 
terior edge, or terminator.” But the luminous border, as I 
have described it, in the observations of the 9th, 16th, 20th, 
and 2 2d of April, does not in the least agree with the above 
representation. 
With regard to the cause of this appearance, I believe 
that I may venture to ascribe it to the atmosphere of Venus, 
which, like our own, is probably replete with matter that 
reflects and refracts light copiously in all directions. There- 
fore on the border, where we have an oblique view of it, 
there will of consequence be an increase of this luminous ap- 
pearance. 1 suppose the bright belts, and polar regions of 
Jupiter, for instance, which have a greater light than the 
faint streaks, or yellow belts, on that planet, to be the parts 
where its atmosphere is most filled with clouds, while the 
latter are probably those regions which are free from them, 
and admit the sun to shine on the planet ; by which means 
we have the reflection of the real surface, which 1 take to be 
generally less luminous. 
If this conjecture be well founded, we see the reason why 
spots on Venus are so seldom to be perceived. For, this 
planet having a dense atmosphere, its real surface will com- 
