on the Planet Venus. 
H5 
At 8 b 20', on the contrary, the difference was no longer by 
far so perceptible.* 
This day the first traces of Venus's twilight shewed them- 
selves ; for the points of the horns appeared to terminate 
beyond the illuminated hemisphere, in an extremely faint 
bluish-grey light. 
May 10th, 6 h 40'. A perfectly similar phase. I found, so as 
to be quite certain of it, the southern horn only half as broad 
as the northern ; but both horns were equally long. 
f 30', still the same. 
8'’ 15'. With 180, 400, and 560 magnifying powers of the 
13-feet reflector, and a distinct image, I found traces of the 
twilight which could not be mistaken. The light grew 
dimmer and dimmer to the point of both horns, and at the 
points was so dim, that it seemed to lose itself in the faint light 
of the sky. A still finer dimmer trace of light shewed itself 
twinkling at both sides, on the edge of the dark hemisphere, 
and including this the two horns comprehended sensibly more 
than a semicircle; but it was too fine and dim for x me to 
measure its extension. 
Even if I had not seen this, I should repeatedly have ob- 
tained conviction of the. particular density of Venus's atmo- 
sphere, by the faint colour of the points of the horns, and of the 
boundary of illumination. 
* It is scarcely necessary to put the reader in mind, that small, undulating, knotty 
inequalities of the boundary of light, in such observations, must not be taken for true 
inequalities, or mountains of Venus. In general, these .small crescents, as the en- 
lightened part lies obliquely to the eye, are not well suited for observing the true ine- 
qualities of the boundary line, or any.spots there may happen to be. For such obser- 
vations, we should be assiduous in attending to the planet, about the time of its 
greatest distance from the sun. 
MDCCXCV. 
u 
