CELESTIAL DAY OBSERVATIONS. 
121 
latitude; cd a segment of the apparent diurnal path of the ObserTBlioM' 
planet j and e f & segment of the sun’s diurnal arc. .Fig. 2. nn Vei'iitt'i 
rrepreseiits the board to be used when the planet is in north the day-tun*, 
daiiiude, which needs no farther description*. — By this means 
Venus may be viewed with ease, ' for several hours about the 
time of her conjunction, and with considerable distinctness, if 
her latitude exceeds 3°, and her elevation above the horizon be 
<COnsi< lei able. 
The circumstance now ascertained, that Venus may be seen 
at the tune of her superior conjunction, may not be considered 
as a fact of much importance in astronomy. It is always useful, 
however, in every department of science, to ascertain every fact 
connected with its principles, however circumstantial and 
tniiiute ; as it tends to give precision to its language, and may 
oltimaiely promote its progress, by leading to conclusions which 
were not at first apprehended. The present fact may possibly 
liead to the determination of the difference (if any) between the 
polar and equatorial diameters of Venus, which has hitherto 
tfem iliied undetermined. It is well known that the earth is of 
I spheroidal figure, lliaving its polar shorter titan its equatorial 
diameter. Jupiter has long been known to exhibit a similar 
6gnre, which is perceptible by a telescope of moderate power ; 
and Dr. Herschel has lately found, that Mars and Saturn are 
also oblate spheroids, and has determined the pro|)ortion 
oetween their equatorial and polar diameters. As Venus 
sevolves about her axis with a swiftness as great as that of the 
sarth, it is reasonable to conclude that she is of a similar figure. 
It is difficult, however, if not imp>o$sible, to determine this point 
oy observation, when she is in those positions in which she has 
most frequently been viewed ; as at such times she assumes 
jither a gibbous phase, or the form of a half-moon, or that of 
I crescent. 1 am, therefore, of opinion, that, at some future 
injunction, when her geocentric latitude is considerable, with 
I telescopic of a high magnifying pow’er, furnished with a 
micrometer, this point might be ascertained. If she is then 
• In this description the observer is supposed to be in north latitude. . 
VoL. XXXVI.— No. I6b. K viewed 
