1/2 
tude of those mountains which, during that 
time, he had an opportunity of examining, 
seems liable to no objection. The rock 
situated near LaCus Niger, was found to be 
about one mile in height, but none of the 
other mountains which he measured proved 
to be more than half that altitude ; and Dr. 
Herschel concludes, that with a very few ex- 
ceptions, the generality of the lunar moun- 
tains do not exceed half a mile in their per- 
pendicular elevation. See Keill’s Astron. 
Lect. x. Phil. Trans. Vo!, nxx. 
do Dr. Herschel also we are indebted 
tor an account of several burning volcanoes, 
which he saw at different times in the moon. 
In the 77th vol. of the Phil. Trans, he says, 
April 19, 10 hours, 36 minutes, sidereal 
time. I perceive three volcanoes in different 
places of the dark part of the new moon. 
Two of them are nearly extinct ; or, other- 
wise, in a state of going to break out, which 
perhaps may be decided next lunation. The 
third shows an actual eruption of fire, or 
luminous matter.” On the next night. Dr. 
Herschel saw the volcano burn with greater 
violence than on the preceding evening. 
He considered the eruption to resemble a 
small piece of burning charcoal when it is 
covered by a thin coat of white ashes, which 
frequently adhere to it, when it has been 
some time ignited; and it had a degree of 
brightness about as strong as that with which 
such a coal would be seen to glow in faint 
daylight. It is not yet determined whether 
there is an atmosphere belonging to the 
moon. See Phil. Trans, for the year 1792. 
d he moon is seen by means of the light 
which comes to it from the sun being re- 
flected from it. Its changes or phases de- 
pend upon its situation relatively to the earth 
and the sun. When the moon is in oppo- 
sition to the sun at A (fig. 7.) the enlighten- 
ed side is turned towards the earth, as a, and 
it appears full. When tire moon is in con- 
junction at E with the sun, its dark side is 
turned towards us, and it is invisible, as at e. 
As it proceeds in its orbit, as at F, a small 
part of the enlightened side is seen, and then 
?ve have what is called a new moon ; and we 
continue to see more and more of the en- 
lightened side, as the moon approaches at 
Cj and H, to the state of opposition or full 
moon. The waning or decreasing of the 
moon takes place in the same manner, but 
in a contrary order. The earth must perform 
the same office to the moon that the moon 
does to us'; and it will appear to the inhabit- 
ants of the moon (if there be any), like a 
very magnificent moon, being to them about 
fifteen times as large as the moon to us, and 
it will also have the same changes or phases. 
Hence it is evident, that one half of the moon 
is never in darkness, the earth constantly 
affording it a strong light, during the absence 
bf the sun; but the other half has a fort- 
night’s light and darkness by turns. 
When the moon is near the first of Aries, 
and moving towards the tropic of Cancer, 
the time of its rising will vary but little for 
several days together. If the moon were to 
move in the equator, its motion in its orbit, 
by which it describes a revolution, in respect 
of the sun, in 29 days, 12 hours, would carry 
it every day eastward from the sun about 
12 degrees 11 minutes, whence its time of 
rising would vary daily about 50 minutes. 
But, because the moon’s orbit is oblique to 
ASTRONOMY. 
the equator, nearly coinciding with the 
ecliptic, different parts of it make different 
angles with the horizon, as they rise or set ; 
those parts which rise with ’ the smallest 
angles setting with the greatest, and the re- 
verse. Now the less this angle is, the greater 
portion of the orbit rises in the same time. 
Consequently, when the moon is in those 
parts which rise or set with the smallest angles, 
it rises or sets with the least difference of 
time, and the reverse. But in northern lati- 
tudes, the smallest angle of the ecliptic and 
horizon is made when Aries rises and Libra 
sets, and the greatest when Libra rises and 
Aries sets ; and therefore, when the moon 
rises in Aries, it rises with the least difference 
of time. Now the moon is in conjunction in 
or near Aries, when the sun is in or near 
Libra, that is, in the autumnal months; when, 
the moon' rising in Aries, whilst the sun is 
setting in Libra, the time of its rising is ob- 
served to vary only two hours in six days in 
the latitude of London. This is called the 
harvest-moon. 
This circumstance takes place every 
month ; but as it does not happen at the time 
of full moon, there is no notice taken of it. 
When the moon’s right ascension is equal to 
six signs, that is, when she is in or about the 
beginning of Libra, there is the greatest dif- 
ference of the times of rising, yiz. about an 
hour and 15 minutes. Those signs which 
rise with the least angle set with the greatest, 
and the contrary; therefore, when there is 
the least difference in the times of rising, 
there is the greatest in setting, and vice versa. 
The following table shews the daily mean 
difference of the moon’s rising and setting, on 
the parallel of London, for 28 days ; in which 
time the moon finishes her period round the 
ecliptic, and gets nine degrees into the same 
sign from the beginning of which she set out. 
Days. 
Signs. 
a 
co 
Grq 
Rising Diff 
Setting Diff. 
CO 
o 
H. 
M. 
H. 
M. 
1 
25 
13 
1 
5 
0 
50 
2 
26 
1 
10 
0 
43 
3 
a 
10 
1 
14 
0 
37 
4 
23 
1 
17 
0 
32 
5 
6 
1 
16 
0 
28 
6 
19 
1 
15 
0 
24 
7 
2 
1 
15 
0 
20 
8 
15 
1 
15 
0 
18 
9 
28 
1 
15 
0 
17 
10 
in 
12 
1 
15 
0 
22 
31 
26 
1 
14 
0 
30 
12 
1 
8 
1 
13 
0 
39 
13 
v? 
21 
1 
10 
0 
47 
14 
4 
1 
4 
0 
56 
15 
17 
0 
46 
1 
5 
16 
1 
0 
40 
1 
8 
17 
14 
0 
35 
1 
12 
18 
27 
0 
30 
1 
15 
19 
X 
10 
0 
25 
1 
16 
20 
23 
0 
20 
1 
17 
21 
T 
7 
0 
17 
1 
16 
22 
S 
20 
0 
17 
1 
15 
23 
3 
0 
20 
1 
15 
24 
16 
0 
24 
1 
15 
25 
29 
0 
30 
1 
14 
26 
n 
13 
0 
40 
1 
13 
27 
26 
0 
56 
1 
7 
28 
25 
9 
1 
00 
1 
58 
The Moon’s motion is subject to many irre- 
gularities, on account of the inclination of its 
orbit to the plane of the ecliptic, and the at- 
traction of the Sun and the other planets. 
Of the superior planets. 
Mars is not so bright as Venus, nor even as 
Jupiter, though nearer to the sun. Its colour 
is a little reddish. Some spots have been ob- 
served upon its surface, from which its rotation 
round its axis, and the inclination of its axis 
to the plane of its orbit, have been deter- 
mined. 
The following particulars respecting Mars 
are given by Dr. Herschel, after long and ac- 
curate observations. 
The axis of Mars is inclined to the ecliptic 
59° 42. 
The node of the axis is in 17° 47' of Pisces. 
The obliquity of the ecliptic on the globe 
of Mars in 28° 42'. 
The point Aries on the Martial ecliptic an- 
swers to our 19° 28 / of Sagittarius. 
The figure of Mars is that of an oblate sphe- 
roid, whose equatorial diameter is to the polar 
one as 1355 to 1272, or as 16 to 15 nearly. 
The equatorial diameter of Mars, reduced 
to the mean distance of the earth from the Sun, 
is 9" S'". 
And that planet has a considerable but 
moderate atmosphere ; so that its inhabitants, 
probably, enjoy a situation, in many respects, 
similar to ours. 
Phil. Trans. Vol. Ixxiv. Part 2. 
Ceres Ferdinandea is a very small planet, 
situated next without Mars : it was discovered 
on the first day of the present century by Mr. 
Piazzi, an Italian astronomer. 
Pallas is another very small planet, disco- 
vered by Dr. Olbers of Bremen, on the 28th 
of March, 1802. Juno is likewise a very 
small planet, discovered by M. Harding, as he 
was engaged at Lilienthal, in examining the 
catalogue of the stars published by M. La- 
lande. This planet and the two former ones. 
Dr. Herschel proposes to call asteroids, be- 
cause they are so much smaller than any of the 
other planets. 
Juno is the twelfth planet discovered within 
these few years. Dr. Herschel discovered 
the planet that goes by his own name, March 
18,1781. In January 1787 he perceived that 
this planet had two satellites, and some time 
after he discovered four others belonging to 
his planet. In the autumn of 1789 he ob- 
served two new satellites belonging to Saturn. 
The Ceres was discovered in 1801 ; the Pallas 
in 1802; and the Juno in 1804. 
Jupiter is the brightest planet next to Venus. 
When viewed by a telescope, several belts are 
observed across its disc, parallel to its equator : 
these belts are variable, and have been sup- 
posed to be ranges of clouds in the atmosphere 
of the planet. They are sometimes of differ- 
ent breadths, and sometimes nearly of the 
same breadth. Large spots have been seen 
in these belts ; and when one of them vanishes, 
the Contiguous spots disappear with it. Dr. 
Herschel has paid attention to the rotation of 
these spots, and has found that the rotation of 
the same spot diminished; thus in February 
1778 one revolved in nine hours fifty-five mi- 
nutes and twenty seconds, but the same spot 
in April revolved in nine hours fifty-one mi- 
nutes and thirty-five seconds. This he observes 
is agreeable to the t heory of equinoctial winds, 
as it may be some time before the spot can 
acquire the velocity of the wind ; and if Ju- 
piter’s spots should be observed in different 
