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A balloon, turning upon its axis as it floats through the atmosphere, affords a sensible representation of the earth in its annual progress round the Sun, which is productive of the various vicissitudes of the seasons, winter, spring, summer, and autumn.

It has likewise been asserted, that if the earth moved, a stone dropped from the top of a tower, or any other high building, would not fall just at the bottom of it, as the building must have advanced considerably forward during the time of the fall. But it is well known, that if a body be projected from another body in motion, it will always partake of the motion of that other body. Thus, a stone dropped from the top of a mast, while the ship is under sail, is not left by the vessel, but falls exactly at the foot of the mast: and thus the atmosphere, as Milton has observed above, is likewise borne along with the earth.

This motion of the earth round its axis is called its diurnal motion, and is that which occasions the regular return of day and night, and all the celestial appearances before mentioned. I could here descant with pleasure on the various beneficial consequences attending this daily revolution; but, as this would lead my present disquisition too far, I shall conclude with the sentiment of the Roman orator: 'Diei noctisque vicissitudo conservat animantes, tribuens aliud agendi tempus, aliud quiescendi. Sic undique omne ratione concluditur, mente, concilioque divino omnia in hoc mundo ad salutem omnium, conservationemque admirabiliter administrari.' And this reference of all things to the benevolent agency of the Supreme Being, is beautifully expressed by Mallet;

Thee, Nature's God!

First Source of all things lovely, all things good!-
Thee all things own! Thou speakest, and it is day.

Obedient to thy nod, alternate night
Obscures the world. The seasons, at thy call,
Succeed in train, and lead the year around.

No. XI.

ON GRAVITY.

Thine these noble works

Great universal Ruler!

Thy virtual energy the frame of things
Pervading actuates; as at first thy hand
Diffused, through endless space, this limpid sky,
Vast ocean without storm, where these huge globes
Sail undisturbed, a rounding voyage each;
Observant all of one unchanging law.
Simplicity divine! by this sole rule,
The Maker's great establishment, these worlds
Revolve harmonious, world attracting world
With mutual love, and to their central sun
All gravitating.

MALLET.

O, unprofuse magnificence divine!
O, wisdom truly perfect! thus to call
From a few causes such a scheme of things,
Effects so various, beautiful and great,
An universe complete.

THOMSON.

MY late inquiries into the Solar System, the Plurality of Worlds, and the Figure and Motion of the Earth, naturally lead me to some considerations on Gravity, which is the most antient and universal property of matter, and that, principally, by which the beauty, order, and harmony of the universe are invariably maintained. The illustrious Newton has pursued his speculations on this subject with such success, that, the most simple nature of gravity being supposed, he has established the true system of the world beyond all controversy, and explained clearly the most considerable phenomena of Nature. And his opinion of the nature and properties of gravity is this:

Every single particle, of all bodies whatever, gravitates to every single particle of all bodies whatever: that is, they are impelled toward each other by the force of gravity.

This gravitating force is universal as to the extent of it; that is, all bodies whatever, so far as we know, wherever they are placed, not only on the earth, but also in the heavens, whether in the Moon or planets, the Sun, or any other place, are endued with this power.

This force is also universal as to the kinds of bodies; that is, all bodies, whatever their figure, form, or texture be; whether they be simple or compound, solid or fluid; whether they be great or small, in motion or at rest; are endued with this power.

This force is also universal as to time; that is, all other conditions being the same, it never increases, nor diminishes.

The quantity of this gravity, at equal distances, is always exactly in proportion to the quantity of matter in the gravitating bodies: for instance, if a cubic foot of gold has a thousand pound weight upon the superficies of the earth, two cubic feet will have two thousand pound weight upon the same superficies; and if the earth contained but half the quantity of matter that it does now, the same cubic foot of gold, that has now a thousand pound weight upon the superficies of the earth, would have five hundred only.

The gravity of given bodies is greater or less, according to the distance of those bodies from each other; for example, a stone which, near the

superficies of the earth, is very heavy, if it could be carried to a distance as high as the Moon, would be very light.

And, finally, the proportion of the increase or decrease of this gravity in bodies approaching to, or receding from, each other, is such, that its force is reciprocal in a duplicate proportion, or as the squares of their distances: for example, a body which, at the distance of ten diameters of the earth, weighs a hundred pounds, would, if its distance were but half as far, weigh four times as much; and if but a third part as far, nine times as much. In like manner, the force which, upon the superficies of the earth, would support a hundred pound weight, if it were twice as far off the centre, could support four times the weight, and, if at three times as far off, could support nine times the weight.

It must be observed, moreover, that the motion. of falling bodies is increased, in successive intervals, in the proportion of odd numbers, 1,3,5,7,9, &c. so that the spaces they run through are as the squares of the times; that is, if a heavy body descended one foot in a second of time, it would descend four feet in two seconds, nine feet in three seconds, &c. Or correctly, at least in the latitude of London, a body falling freely, passes through 16's feet in the first second; four times 16, or 64 feet, in the first two seconds; nine times 16, or 144 feet in the first three seconds; and so on.

Such are the principal properties of gravity, from the observation of which our immortal Newton deduced his sublime theory of the universe. It may be pleasing to the reader, to know the very simple incident, which, leading to the most extensive and complicated calculations, was productive of these noble and wonderful discoveries... It is thus related, on the authority of his friend and commentator, Dr. Pemberton:

Happening one day, in the year 1666, when only twenty-five years of age, to be sitting under an apple tree, an apple falling upon his head, suggested a variety of reflections. The phenomena of falling bodies in particular engaged his attention; and, extending his researches to the heavens, he began to investigate the nature of motion in general. Because there is motion, he reasoned, there must be a force that produces it. But what is this force? That a body, when left to itself, will fall to the ground, is known to the most ignorant; but if you ask them the reason of its thus falling, they will think you either a fool or a madman. The circumstance is too common to excite their wonder, although it is so embarrassing to philosophers, that they think it almost inexplicable.

It is impossible to follow this great philosopher through all his reasonings; but we may recapitulate some of the principal phenomena of this simple, yet wonderful, this obvious, yet mysterious law of nature. If I take a stone, and let it drop from my hand, it falls immediately to the ground, and would fall still farther, if there was a hole in the earth, and nothing to prevent its passage. In like manner, when a stone, or any other substance, is placed upon a table, it presses the table with the same force by which it would fall to the ground, if left to itself; and when a body is suspended at the end of a string, the force that impels it downward, stretches the string, and, if it be not sufficiently strong, will break it.

The cause of this falling propensity in all bodies, whatever it be, is called Gravity, Gravitation, or Attraction; and when a substance is said to be heavy, nothing more is meant, than a reference to the tendency which it has to fall to the ground,

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