m. S.

Tuesday, March 1, to the time on the dial ADD 12 481

Sunday,

Friday, Wednesday,

Monday,

Saturday,

6, 11,

16,

21,
26,

11 37

For true

The Georgian planet will be stationary on the 6th. The Sun enters the sign Aries at 37 minutes after 5 in the morning of the 21st. The planet Mercury will be found stationary on the 23d.

The Moon will be at the full at 15 minutes past 7 in the morning of the 6th: it enters the last quarter at half past one in the morning of the 14th. The succeeding new Moon or change will happen at 6 minutes past 9 in the evening of the 21st, and this enters its first quarter at 21 minutes past 5 in the afternoon of the 28th.

The time of the Moon's rising for the first five days after she is in the full will be as follows, viz. on the 7th of March, 5 min. past 7 in the afternoon.

8th, 9th, 10th,

19 31

8

ditto.

11th,

On the 1st day of March, the Moon will eclipse the star marked. The immersion will occur at 32 minutes past 7 in the evening, when the star will be 5 north of the Moon's centre: the emersion happens 43 minutes past 8, the star being at that time 3 minutes north of the Moon's centre.

Mercury's greatest elongation from the Sun happens on the 16th.

In the eclipses of the first satellite of Jupiter, that will be visible in London this month, the emersions will occur at the following times, viz. on the

7th day, at 29 m. past 1 in the morning.

VIEW OF THE SOLAR SYSTEM.

Of Mercury.

Of the eleven planetary bodies already mentioned, Mercury and Venus are called inferior planets; the others are denominated superior planets.

The inferior ones are so named, because they both revolve in orbits that are included within the orbit of the earth, which fact has been ascertained by observation; for by watching the progress of these bodies, it is found that they are continually changing their places among the fixed stars, and that they are never seen in opposition to the Sun; that is, they are never seen in the western side of the heavens in the morning, when the Sun appears in the east; nor in the eastern part of the heavens in the evening, when the Sun appears in

the west.

To begin with Mercury, which is the nearest to the Sun. This planet is, to an inhabitant of the earth, never seen at a greater distance than about 28 degrees from the Sun, or about as far as the Moon appears to be from the Sun on the second day after the change. On this occount he is seldom visible to us; and when we do get a sight of him, it is for so short a time, and in twilight, that sufficient observations have not been made to ascertain whether this planet has a diurnal motion on its axis; though there is little doubt on the subject.

Mercury's mean distance from the Sun is nearly 37 millions of miles, and its real diameter is 3180 miles; so that the real diameter of Mercury to that of the earth is as 2:5; and the density of Mercury being to that of the earth in the proportion 2.5833 to 1, the quantity of matter in Mercury will be to that in the earth as 0.16536 to 1, or about the th part only; for the quantities of matter in spherical bodies are as the cubes of their diameters and densities.

conjointly'. The weights of equal bodies, on the surfaces of Mercury and the earth, are as 1.0333 to 1, such weight always varying as the diameters and densities conjointly 2.

As the intensities of light and heat, which the planets receive from the Sun, vary inversely as the squares of their distances from the Sun, and as the proportional distances of Mercury and the earth are as 37 to 95 or as 4 to 10, the inverse squares will be as

ties of light and heat at Mercury and the earth.

Mercury changes its phases, like the Moon, according to its several positions with regard to the Sun and earth; except only that he never appears quite full, because his enlightened side is never turned directly towards us, but when he is so near the Sun as to be lost to our sight in his beams. And as his enlightened side is always towards the Sun, it is plain that he shines not by any light of his own, for if he did he would constantly appear round. The length of Mercury's year, or the time he takes in revolving about the Sun, is 88 days, and he travels at the rate of 105.000 miles in an hour3.

When Mercury begins to appear in the evening, it is, as we have observed, with great difficulty distinguished in the rays of twilight: it disengages itself more and more in the following days; and after arriving at about 22° or 23° from the Sun, it returns towards him again. In this interval, the motion of

Mercury with respect to the fixed stars is direct, but when returning it comes within the distance of 18° of the Sun, it seems stationary; after which its motion appears retrograde; it continues to approach the Sun, and is again, in the evening, lost in his rays. After continuing some time invisible, it is seen again in the morning, disengaging itself from the Sun's rays, and departing from the Sun; its motion is still retrograde, as it was before its disappearance: it afterwards becomes apparently stationary, and then resumes its direct motion; its distance increases, it then returns, and, disappearing in the morning in the light of the dawn, is soon after seen again in the evening, producing the same phenomena as before. The extent

of the greatest digressions of Mercury from the Sun, on each side, varies from 16° 12' to 29°. The length of its entire oscillation, as it has been called, or the return to the same position relatively to the Sun, varies likewise from 136 to 130 days.

A long series of observations was no doubt necessary to recognize the identity of Mercury as a morning and evening star, and which for a considerable time was regarded as two distinct bodies, that were alternately seen in the morning and evening to depart from and return to the Sun; but as the one never showed itself till the other disappeared, it was at last suspected to be the same planet which thus oscillated on each side the Sun.

The apparent diameter of Mercury is very variable, and its changes are evidently connected with its relative position to the Sun, and the direction of its motion. It is the least either when the planet in a morning immerges into the solar rays, or when in the evening it disengages itself from them; it is at its maximum when it immerges into the Sun's light in an evening, or when it becomes visible in the morning. It occasionally happens that during the interval of its disappearance in the evening, and its re-appearance

in the morning, it is seen projected in the form of a black spot upon the disk of the Sun, on which it describes a chord. This is called a transit of Mercury, and is, in fact, a real annular eclipse of the Sun; and from this we infer that the light of the planets is borrowed from that body.

The diameter of the Sun, viewed from Mercury, would appear between two or three times as big as it appears to us, that planet being so much nearer to him than we are; and therefore the Sun's disk would appear 6 times as large as to us. The best opportunities that we have of making observations on this.. planet, are those when it is seen on the Sun's disk, to which we have just now referred; in this situation it is only observable with a telescope. The node from which Mercury ascends northward above the ecliptic is in the 15th degree of Taurus, and of course the opposite is in the 15th degree of Scorpio. The earth is in these points about the 6th of November, and the 4th of May; and when Mercury comes to either of his nodes at his inferior conjunction about these: times, he will appear to pass over the disk of the Sun. The first observation of this kind was that of Gassendi, in November 1631.

To an inhabitant of Mercury the solar spots will appear to traverse his disk sometimes in a right line from east to west, and sometimes elliptically. As all the other planets are above Mercury, its phenomena to them will be nearly the same as to us. Venus and the Earth, when in opposition to the Sun, willshine with full orbs, and afford a noble light to that planet.