124 
CELESTIAL DAY OBSERVATIONS. 
Observations 
upon tl.e pla- 
net Venus in 
the day-Uuie. 
day-time, appears from some of the observations of Cassini, 
who saw one of her spots when the sun was more than eight 
degrees above the horizon*. Nor do I consider it altogether 
impossible that her satellite (if she have one, as some have 
supposed) may be detected in the day-time, wlien she is in 
a favourable position for such an observation ; particularly 
W'hen a large portion of her enlightened surface is turned to- 
wards the earth, and when her satellite, of course, musl present 
a similar phase. If this supposed satellite be about one-third 
or one-fourth of the diameter of its primary, as Cassini, Short, 
and Montaigne, supposed, it most be nearly as large as Mer- 
cury, which has been frequently seen in day-light. If such 
a satellite has a real existence, and yet undisLlnguishable in 
day-light, its surface must be of a very different quality for 
reflecting the rays of light, from that of its primary j for it is 
obvious to every one who has seen Venus with a high power, 
in the day-time, that a body of equal brilliancy, though four 
times less in diameter, would be quite perceptible, and exhibit 
a visible disk. Such observations, however, would be made 
with a greater effect in Italy, and other southern countries, 
where the sky is more clear and serene, and where the planet 
may be viewed in higher altitudes than in this island. 
5. Another conclusion, from the observations on Venus, is, 
that a moderate diminution of aperture is useful, and even ne- 
cessary, in viewing this planet when near the sun. Its effect 
is owing, in part, to the direct solar rays being thereby more 
effectually excluded. 
In fine, we may fairly conclude, that such expressions of 
astronomical writers, when describing the phases of V>nus, as 
those quoted above, are but partially true, and therefore ought 
either to be laid aside, or qualified, if they would not run the 
risk of conveying an erroneous idea. The vague and incorrect 
expressions and statements not only in this, but in several other 
respects, which abound in several late popular writings on astro- 
• See Long's Astronomy, vol. 2, p. 487, or Encyclopaedia Rritannira, 
Tol. 2 p, 436. 3d edition. 
