ASTRONOMY. 
357 
ed, gibbous, See. her illuminated part being conftantly 
turned toward the Sun, or directed towards the eaft when 
the is a morning ftar, and towards the weft when an even¬ 
ing ftar. 
Callini and Campani, in the years 166 5 and 1 666, difco- 
vered (pots in the face of Venus : from the appearances of 
which the former afcertained her motion round her axis; 
concluding that this revolution was performed in let's titan 
a day ; or at lcaft that the bright fpot which he obferved 
finithed its period either by revolution or libration in about 
twenty-three hours. And De la Hire, in 1700, through 
a telefcope of fixteen feet, difcovered fpots in Venus; 
which he found to be larger than thole in the Moon. The 
next obfervations of the fame kind that occur, are thofe 
of Signior Bianchini at Rome, in 1726, 1727, and 1728, 
who, with Campani’s glades, difcovered feveral dark fpots 
in the dilk of Venus, of which he gave an account and a 
reprefentation in his book entitled Hefperi et Phofphori 
Nova Phenomena, publilhed at Rome in 1728. From fe¬ 
veral fuccelTive obfervations Bianchini concludes, that a 
rotation of Venus about her axis was not completed in 
twenty-three hours, as Cadini imagined, but in 247 days; 
that the north pole of this rotation faced the twentieth de¬ 
gree of Aquarius, and was elevated 15 0 above the plane 
of the ecliptic, and that the axis kept parallel to itfelf, 
during the planet’s revolution about the Sun. Cadini the 
fon, though he admits the accuracy of Bianchini’s obfer¬ 
vations, difputes the conclufion drawn from them, and fi¬ 
nally obferves, that if we fuppofe the period of the rota¬ 
tion of Venus to be 13!!. 20' it agrees equally well with 
the obfervations both of his father and Bianchini; but, if 
Hie revolve in 24d. 8h. then his father’s obfervations mult 
be rejected as of no confequence. 
In the Philof. Tranf. 1792, are publilhed the refults of a 
courfe of obferyations on the planet Venus, begun in the 
year 1780, by Mr. Schroeter, of Lilienthal, Bremen. From 
thefe oblervations, the author infers that Venus has an at- 
mofphere in fotne refpeCts fimilar to that of our Earth, but 
far exceeding that of the Moon in denfity, or power to 
weaken the rays of the Sun : that the diurnal period of 
this planet is probably much longer than that of the other 
planets: that the Moon alfo has an atmofphere, though 
lefs denfe and high than that of Venus: and that the 
mountains of this planet are five or fix times as high as 
thofe on the Earth. Dr. Herfchel too, between the years 
1777 and 1793, has made a long feries of obfervations on 
this planet, accounts of which are given in the Philof. 
Tranf. for 1793. The refults of thefe obfervations are : 
that the planet revolves about its axis, but the time of it 
is uncertain : that the pofition of its axis is alfo very un¬ 
certain : that the planet’s atmofphere is very confiderable: 
that the planet lias probably hills and inequalities on its 
furface, but he has not been able to fee much of them, 
owing perhaps to the great denfity of its atmofphere; as 
to the mountains of Venus, no eye, he fays, which is not 
conliderably better than his, or adilted by much better in- 
ftruments, will ever get a fight of them: and that the ap¬ 
parent diameter of Venus, at the mean diftance from the 
Earth, is 1S" - 79 ; from whence it may be inferred, that 
this planet is fomewhat larger than the Earth, inftead of 
being lefs, as former altronomers have imagined. 
In 1672 and 1686, Cadini, with a telefcope of thirty- 
four feet, thought he law a fatellite move round this pla¬ 
net, at the diftance of about three-fifths of Venus’s dia¬ 
meter. It had the fame phafes as Venus, but without any 
well-defined form ; and its diameter fcarcely exceeded one- 
fourth of the diameter of Venus. Dr. Gregory ( Aftron. 
lib. vi. prop. 3.) thinks it more than probable that this 
was a fatellite; and fuppofes that the reafon why it As not 
more frequently feen, is the unfitnefs of its furface to re¬ 
flect the rays of the Sun’s light; as is the cafe of the fpots 
in the Moon; for, if the whole dilk of the Moon were 
compofed of fucli, he thinks Hie could not be feen fo far 
as to Venus. 
Mr. Short, in 1743, with a reflecting telefcope of i 6 } s 
Vou II. No.76. 
inches focus, perceived a fmall ftar near Venus : with ano¬ 
ther telefcope of the fame focus, magnifying fifty or fixty 
times, and fitted with a micrometer, he found its diftance 
from Venus about 10'; and, with a magnifying power of 
240, he obferved the ftar adiime the fame phafes with Ve¬ 
nus; its diameter feemed to be about one-third, or fome¬ 
what lefs, of the diameter of Venus; its light not fo bright 
and vivid, but exceeding (harp and well-defined. He 
viewed it for the fpace of an hour; but never had the good 
fortune to fee it after the firft morning. Philof. Tranf. 
No. cccclix. p. 646, or Abr. vol.viii. p. 208. 
M. Montaign, Of Limoges in France, preparing for 
obferving the tranlit of 1761, difcovered in the preceding 
month of May a ltnall ftar, about the diftance of 20' from 
Venus, the diameter being about one-fourth of that of 
the planet. Others have alfo thought they faw a like ap¬ 
pearance. And indeed it mull be acknowledged, that Ve¬ 
nus may have a fatellite, though it is difficult for us to fee 
it. Its enlightened fide can never be fully turned towards 
us, but when Venus is beyond the Sun ; in which cafe 
Venus herfelf appears little bigger than an ordinary ftar, 
and therefore her fatellite may be too fmall to be perceived 
at fuch a diftance. When fhe is between us and the Sun, 
her Moon has its dark fide turned towards us; and, when 
Venus is at her greateft elongation, there is but half the 
enlightened fide of the Moon turned towards us, and even 
then it may be too far diftant to be feen by us. But it was 
prefumed, that the two tranfits of 1761, and 1769, would 
afford opportunity for determining this point; and yet we 
do not find, although many obfervers directed their atten¬ 
tion to this objeCt, that any fatellite was then feen in the 
Sun’s diflc; unlefs we except two perfons, viz. an anony¬ 
mous writer in the London Chronicle of May 18, who fays, 
that he faw the fatellite of Venus on the Sun the day of 
the tranfit, at St. Neot’s in Huntingdonfhire; that it mo¬ 
ved in a track parallel to that of Venus, but nearer the 
ecliptic; that Venus quitted the Sun’s dilk at thirty-one 
minutes after eight, and the fatellite at fix minutes after 
nine; and M. Montaign of Limoges, whofe account of 
his obfervations is in the Memoirs of the Academy of Pa¬ 
ris, from udience the following certificate is extracted : 
Certificate. “ We having examined, by order of the 
academy, the remarks of M. Baudouin on a new obferva- 
tion of the fatellite of Venus, made at Limoges the nth 
of May by M. Montaign—This fourth observation, of 
great importance for the theory of the fatellite, has fhewn 
that its revolution muft be longer than appeared by the 
firft three obfervations. M. Baudouin believes it may be 
fixed at twelve days; as to its diftance, it appears to him 
to be fifty femi-diameters of Venus; whence he infers, 
that the mafs of Venus is equal to that of the Earth. This 
mafs of Venus is a very effential element to aftronomy, as 
it enters into many computations, and produces different 
phenomena, See. Signed, /’ Abbe de la Caille. 
De la Lande.” 
Of the Phenomena peculiar to the inferior Planets, 
Venus and Mercury. 
There are two different fituations, in which an inferior 
planet will appear in conjunction with the Sun ; one when 
the planet is between the Sun and the Earth, and the other 
when the Sun is between the Earth and the planet. Let 
A, in the following figure, be the Earth in its orbit; E, 
the place of Venus in her orbit EHG ; S, the Sim; and 
FVPORT'D, an arc in the ftarry heavens. In this litua- 
tion the Sun and Venus are on the fame fide of the Earth, 
and will appear in the fame point of the heavens, fo as to 
be in conjunction. If the Earth is at A, and Venus at G, 
they will alfo appear to be in conjunction. If the Earth 
is at A, the Sun at S, the planet at E, nearer to the Earth 
than the Sun, it is called its inferior conjunction. But, if 
the Earth is at A, andvthe planet at G, farther from the 
Earth than the Sun, this is called th efuperior conjunction 
of the planet. 
If an inferior planet is at F,, the Earth at A, arid the 
4 Y Cm a 
