.0208; the size, mass, and density of the Earth being respectively considered as unity, or 1. And a body weighing 1 pound on the surface of the earth, would weigh.95 on the surface of Uranus.

TABLE,

Showing the mean distance of Uranus from the Sun, &c.

Mean distance in miles,

Eccentricity of its orbit,

Long. of ascending node Jan. 1st, 1801,
Long. of the perihelion at the same time,
Heliocentric long. at the same time,
Geocentric long. at the same time,

Greatest equation,

Mean daily motion in its orbit,

1,812,413,975

The sidereal motion of the apsides is about 3' 59" in a century; but the tropical motion is 10 27' 29", according to the order of the signs.

The place of the nodes has a retrograde motion of 59' 58" in a century; but, owing to the recession of the equinoctial points, their apparent motion is direct in the same time.

The inclination of the orbit is subject to a small increase of about 3" in one hundred years.

The greatest equation has a secular increase of about 11 seconds.

The intensity of light or heat on this distant planet is to that on the earth, with regard to the influence of the sun's rays, as 276 to 100,000, or as 1 to 362 nearly.

3. Dr. Herschel has discovered six satellites moving round Uranus, in orbits which are nearly in the same plane, and almost at right angles to the orbit of their primary.

Two of these satellites were discovered in 1787, and the other four in 1790 and 1794.

The periodic revolutions and the distances of these satellites, from the body of Uranus, expressed in semi-diameters of that planet, as well as in miles, are exhibited in the following table :

Some astronomers imagine that the motion of these satellites is from east to west, or directly the reverse of all the planets, and other satellites; but this doubtless is an optical illusion, arising from the difficulty of ascertaining which part of the orbit inclines to the earth, and which declines from it. The inclination of their orbits, and the place of their nodes, are not correctly ascertained.

According to Dr. Brinkley, the relation of the periodic times, and distances of the satellites from their primary, hold in all the secondaries of each planet respectively.

It may also be observed, that the rotation of the sun and planets are all in the same direction.

QUESTIONS.

What is the length of the day on the surface of Uranus ?

What is the diameter of Uranus in miles; and what its apparent diameter ?

What is the relative mean distance of Uranus from the sun, with respect to the earth?

How many satellites has Uranus, and by whom were they discovered?

The following TABLE exhibits at one view the principal outline of the Planetary System.

The times and arcs of retrogradation are computed on the supposition that the orbits are circular. The apparent diameters of the new planets have not, according to Dr. Brinkley, been yet ascertained. They are too small to be measured by micronometers. Dr. Herschel thinks that if the diameter of any one of them amounted to of a second, he should have been able to have ascertained it.

It may be observed, that an apparent diameter of of a second, in opposition, would give a real diameter of 65 miles. Perhaps the most striking circumstance in the above table, is the great velocity with which the planets move; and this is more impressed, when we consider that of the earth on which we live, the velocity of which is 90 times greater than the velocity of sound. In contemplating these velocities, it cannot but occur to us, how great a power is necessary to be continually acting, to circumflect the planets about the sun, and compel them to leave the tangential direction. A power that acts incessantly, and is able to counteract the great velocities of the planets, must excite our inquires as to its origin and law of action.

We can ascertain that this power is constantly directed towards the sun, increases in intensity as the square of the distance from the sun decreases, and that it is the same power which is diffused through the whole planetary system, only varying in quantity as the square of the distance from the sun is varied. So far physical astronomy teaches us; but the proximate cause of this power, or solar gravity, as it may be called, is unknown. We cannot trace by what agency the Supreme Being, from whom all things originate, has ordained the operations and laws of gravity to be executed.

By a comparison of the distances and periodic times, which are determined independently of each other, it will be seen, as has already been observed, that the square of the periodic times are as the cubes of the distances. This relation was first found out by Kepler. For a long time no necessary connexion was discovered between the periodic times and distances, till at last it was shown to be a consequence of the law of gravity above-mentioned. At present we know of no secondary cause that could have any influence in regulating the respective distances of the planets from the sun; yet there appears a relation between the distances, that cannot be considered as accidental. This was first observed by Professor Bode, of Berlin, who remarked that a-planet vas wanting, at the distance at which the new planets have ince been discovered, to complete the relation.