As any body considered in mechanics, is only an aggregate of several other bodies or parts, so the centre of gravity of a body, is only the common centre of gravity of all its parts; and consequently, if several bodies are united in one machine, or there be any combination of bodies to be sustained, we are no longer to regard the particular centres of gravity of the compound, but only the common centre of gravity of the whole. Thus a windmill should be supported under the common centre of gravity of all its parts, and its line of direction should coincide with the axis of the post around which it moves; and a crane on a wharf or dock, when the machine turns round, should have the line of direction in its axis.

The name of a system does not purposely belong to any unconnected assemblage of particles, but can only be applied to such collections of them, as are joined together by the mechanical forces. The varieties in such connecting forces are innumerable; but we only in this place consider the motions of such systems, where particles are united by mutual and equal forces.

"

The centre of gravity of a system of bodies, will not be disturbed by their mutual attractions; as the motions thus communicated are always equal and opposite; hence the centre of gravity of our planetary system is either at rest, or moves on uniformly in a straight line. The latter is supposed by Dr. Herschel to be the case, from the change which has been observed in the relative situations of some of the fixed stars. Hence also, the centre of gravity of the earth is not affected by the motions on its surface, or within its bowels: when a cannon ball, for instance, is thrown upwards, the projecting force, reacting on the earth, causes it to move in a contrary direction; but as the motions are equal, the centre of gravity remains the same. In general, the actions of bodies on each other, depend not on their absolute, but relative motion, which is the difference of their absolute, when they have the same direction, but their sum, when they are moved in opposite directions.

The stability of a body on an horizontal plane, depends on

the position of the line of direction relative to the base of the body; the nearer this line approaches the centre of the base, the more firmly the body stands, and the contrary, as we daily are shewn by personal experience. When a man is standing, the line of direction falls directly between his feet; when he walks, his natural endeavor is to preserve this line in the same position. If one stand with the feet at a little distance asunder, the attitude is more favorable to steadiness, than when the feet are close together. It is impossible to rise from a chair, without thrusting the head forwards, and drawing the feet backwards at the same time, until the centre of gravity be thrown forward of the feet, when one or both of them must be brought forward to prevent the body from falling to the ground. In walking up a steep hill, a man advances his body and presses only on his toes, or the fore part of his feet, so that the centre of gravity may be preserved in its proper line, and prevent his falling backward. A soldier, laden with a knapsack for the same reason inclines forward, and marches with a firm step so long as his chest is sufficiently advanced to counterpoise the weight on his back, that would otherwise throw the line of direction in the rear of his heels. In an usual and unstudied manner of walking, the foot from which we set off, is our base at first, until by turning the ball of it round, we have thrown the centre of gravity forward beyond it, by which means we should certainly fall, if we did not raise the other leg from the ground, and set it before us, so as to catch ourselves upon it, as upon a prop or support to prevent our tumbling down. This is taking one step; in order to take another, the centre of gravity must be brought directly over the prop; that is, the foot which we set before us, must be made the base from which we take our second step. Hence in walking, the line of direction passes through each foot alternately, and if we set one foot directly before the other, in every step that we take, then this line will move evenly forwards; but if we straddle as we walk, then the line of direction is carried out, first to one side, then tojanother, at the same time that it goes forward, which is the

t

reason why those who step widely have an awkward gait, and are said to waddle. Thus ducks, and most aquatic fowls, whose legs are set at a distance from each other, have an ungraceful motion on land; while the ostrich, the stork, and the peacock, walk directly forward, with their bodies evenly supported

In carrying a load, a man always leans so as to bring the centre of gravity between his feet, and therefore stoops in a direction contrary to his burden. In almost every instance of our motions, we are obliged to use the arts of balancing, to keep ourselves on our feet and it is a useful study for the painter or statuary to know how far the human figure may be bent without losing its centre of gravity.

Remainder next month.

"If to my share some trifling errors fall,
"Look in my FACE, and you'll forget them all!"

POPE..

MR. CENSOR,

You have enchanted me! In spite of the eloquent and impetuous Burke, the age of chivalry has not yet gone! You are the champion of ancient virginity, the warm friendof an honorable though neglected class of females! The wicked and abominable inuendo of Dr. Johnson, "If matrimony has few enjoyments, celibacy has none," is like poison to my burning imagination. He was an admirer of women, and he admired their silence. How few are there who have wisdom enough to appreciate the advantages of a single life. Your encomiums on that state have warmed me into enthu

siasm, into rapture. And since you have generously espous ed my cause, I cannot resist ingenuously opening my whole heart to you, and making you completely acquainted with my personal charms. Madam ****** formerly described

herself to the divine, the pathetic Rousseau, but with such warmth of coloring, and such a captivating grace, that surprises and at once enchains the heart.

Candor has marked every feature of my life. You alrea dy know that I am turned of fifty; but I have not a wrinkle about me. I believe Ariosto begins his famous description of Alcina, the enchantress, with the charms of her face. Shall I too adopt that method? Then, my forehead is low, and my nose, which is aquiline, of considerable length. My eyes are black and full of fire, with long silken lashes. The distance between my nose and mouth does not exceed a quarter of an inch. My lips are ruby-colored, and my mouth wide. Three front teeth have vanished. My chin long; cheeks rosy, and ears large; thus, you will conjecture, the tout ensemble must have a pleasing effect. My neck I must acknowledge is a little skinny, in consequence of which I generally wear a neckcloth. When standing, my form is somewhat elegant, though I am only five feet high. My legs are unfortunately a little shorter than they should be, being twisted, so that when sitting, I appear to be much taller than I really am. The fact is, that whether sitting or standing, I am about the same respectable height. For the benefit of bathing, I have shaved my head, and I always wear a scratch wig. My dress is plain, but uncommonly neat, and for a cœstus I bind a black ribbon round my taper waist. Is this description picturesque? Can you see me distinctly in your" mind's eye?" But what are personal attractions?

"Tis not a set of features or complexion,
The tincture of a skin that we admire!
Beauty soon grows familiar to the lover!
Fades in the eye, and palls upon the sense!!

Jane Wormwood is not to be "pleased with a rattle, and tickled with a straw." She spurns the insignificant from her presence. All the fluttering race of coxcombs inevitably meet with her bitter reproaches and contempt. And why? Because they are intellectually inferior beings, possessing merely instinct. The delicious sensations produced by the

consciousness of eminently good qualities, never can enter their bosoms. Though I can speak Greek "as naturally as pigs squeak," (so say Hudibras) Portuguese, Italian, Spanish, German, and French, I make no boast of it! I only speak of facts; and I am certainly justifiable in recounting my acquirements and propensities, if they are a secret to the world besides!! Jane Wormwood was not born to "waste her sweetness on the desert air." She was born to inherit the splendid literary fame of her father, Jonathan Wormwood, who was,-God rest his soul,-I had almost said, a bachelor. He wrote twenty volumes, folio, on the muscular pow ers of a flea!

VOL. I.

Since my last communication I have been extremely indisposed. My little dog was supposed to be mad. He maliciously bit my finger; I was under the most dreadful apprehension of hydrophobia! I even felt the fever burning in every vein. I conceived an abhorrence to all liquids. The sight of them almost drove me to distraction. My neighbor, Mrs. Crump, vowed that the spinster was mad. She is a married woman. I often contrast her miserable life with my own. She invariably loses by the comparison. The more I think of my own forbearance, chastity, fortitude, and my zeal in resisting the insidious approaches and machinations of men, the more I admire myself. There is nothing in the scale of human misery so ponderous as matrimony. You see what it is, to have a mind so completely elastic as to bend into itself, and approve its own maxims. I can sit the whole day in admiration of the sketches of my own fertile genius! Happy, happy Jane!

Am I an insulated, disconsolate being? You, Mr. Censor, can say, no! Pour l'amour de Dieu ! Should any creature dispute my asseverations, call forth your chivalric spirit, in defence of an honorable damsel. Accept the warmest platonic affection and gratitude of

JANE WORMWOOD.

18