bled to form a judgment of the weight of the mat-ing that it extends to the fixed stars, and, very ter of which the body of the earth is composed. probably, the small variation of place observed in It has been found to be four or five times as much Arcturus, Sirius, and some others, may be occaas it would be if the whole earth were composed sioned by their mutual attraction. of water. As no stone with which we are acquainted weighs so much, and as most metals weigh more, it is probable that the shell of the earth is composed of some metallic ore.

An experiment, by Mr. Cavendish, with balls of lead of an immense size, gave nearly the same result as to the probable weight of the earth.

When a body is propelled forward, as by the discharge of cannon, it will go on, except so far as it is prevented by the resistance of the air, at an equal rate every moment of time, in the direction in which it is sent, and at the same time will fall from the straight line sixteen feet one inch the first second, forty-eight feet three inches the second second, eighty feet five inches the third second, and go on. If several cannon of different range be fired from the top of a cliff or fortification in a direction parallel to the horizon, the balls will all come to the water or plain at the same instant, al

though at different distances. A greater force makes the ball fly farther, but makes no difference in the time it comes to the ground.

As some sort of experiment impresses a fact upon the mind, lay a small marble near the edge of a table, and then striking it with a large one, in the usual way, both will be seen to come to the ground at the same instant. If, from the top of a house or of a high cliff, several boys, at once, by word of command, throw stones parallel to the horizon, though some will go farther than others, all will come to the ground at once.

All bodies, however different in weight, fall to the ground equally fast, unless disturbed by the resistance of air. Get several pieces of lead, or several stones of unequal weight, and let them fall together from the top of a house, they will all come to the ground at the same time.

When bodies have but small weight in proportion to their bulk, the resistance of the air makes a great difference in the time in which they come to the ground, Hence feathers and leaves of trees descend very slowly. By means of an air-pump it may be shown that in a vacuum a feather falls as fast as a guinea. Run a nail through a piece of cork, and cut away part of the cork until it just sinks in the water. Take this and another nail and drop both into water together, the one will fall to the bottom instantly, the other very slowly. Drop both in the air and they come to the ground together, the resistance of the air being to these bodies but inconsiderable. So also a feather, which in air falls but slowly, in a vacuum falls as fast as a guinea.

GRATE. A frame of iron bars, used for burning coal or fuel. Grates are commonly smaller than fireplaces intended for the consumption of wood, on account of the greater heat emitted by coal. Those used for burning anthracite should be made deeper and of a greater height than others, so as to present a comparatively small surface to the air; for, in very cold weather, the air conducts the heat from the surface faster than combustion renews it, so that, if the amount of surface exposed be large, the fire will go out. This kind of coal yields no visible smoke. The chimney, however, should be large enough to transmit smoke, otherwise some of the carbonic acid, which is formed during the combustion, will be sent into the room. This gas is the suffocating vapor of burning charcoal.

GRAVITY. In Physics, the natural tendency or inclination of bodies towards a centre. Terrestrial gravity, is that force by which all bodies are continually urged towards the centre of the earth. It is in consequence of this force that bodies are accelerated in this fall, and when at rest they press the body or that part of the body by which they are supported. As to the cause of gravity, or its nature, nothing whatever is known, and it would be useless and unprofitable to occupy any part of this article in detailing the several vague hypotheses that have been advanced to account for this most important law of nature. All that can be said is, that it appears to be an essential property of matter, or, at least, of all matter that has hitherto become the object of human investigation, though it is by no means certain that matter may not exist which is not subject to its influence. Specific gravity, is the relative gravity of any body or substance, considered with regard to some other body which is assumed as a standard of comparison, and this standard, by universal consent and practice, is rainwater, on account of its being less subject to variation in different circumstances of time, place, &c., than any other body, whether solid or fluid. And, by a very fortunate coincidence, at least to English philosophers, it happens that a cubic foot of rainwater weighs one thousand ounces averdupois; and consequently, assuming this as the specific gravity of rain-water, and comparing all other bodies with this, the same numbers that express the specific gravity of bodies, will at the same time denote the weight of a cubic foot of each in averdupois ounces, which is a great convenience in numerical computations.

The attraction of gravitation was shown by Newton to extend beyond the range of our earth, and to be a principle probably inherent in universal GRAZIER. In Agriculture, a term commonly nature. By it the moon is kept from flying off applied to such farmers as are engaged in the art from the earth into space. By it also the satellites and business of fattening various sorts of live stock of Jupiter, Saturn, and Herschel, are kept near on pasture and other grass-lands. That this sort their primaries. The comets are also under its of business may be managed to the best possible influence. It takes place between different planet- advantage, the grazier should have a perfect knowary bodies, as also their satellites, so as to make a ledge of the nature, properties, and value of all small derangement in their orbits when they come sorts of cattle and sheep stock, as well as of the near to each other. We have no reason for doubt-quality of the ground on which they are to be fed,

pay and receive in large bargains; and among a To remedy this inconvenience, Mr. Nicholson nation so full of fraud as the Chinese, it is no won-made the following experiment:-He procured a der that these are often adulterated with too great Newcastle grind-stone of a fine grit, ten inches in an alloy of copper. They pass, however, in this diameter, and a mahogany block, to be used with state in the common payments. There are some emery on it; both mounted on an axis, to be applied occasions, however, such as the paying of the taxes between the centres of a strong lathe. Both were and contributions, on which they must have their of the same diameter, and turned truly cylindrical. silver pure and fine; on this occasion they have The face of the mahogany block was grooved obrecourse to certain people whose sole business it is liquely in opposite directions, to afford a lodgment to refine the silver, and separate it from the copper for the emery: the face of the stone was smooth, and the lead it contains. This they do in furnaces and a trough with water was placed below it. The made for the purpose, and with very convenient wooden cylinder was faced with oil and emery. vessels. While the copper is in fusion, they take The tool to be ground was a file, from which it a small brush, and dip the end of it into water; was intended to grind off all the teeth. The vethen striking the handle of the brush, they sprinkle locity of the rotation produced by the lathe was the water by degrees upon the melted copper; a so great as to turn the apparatus above five revosort of pellicle forms itself by this means on the lutions in a second. Yet the stone operated but surface of the matter, which they take off while slowly, and the trough was quickly exhausted; so hot with pincers of iron, and immediately throwing that the workman was obliged to slacken the veit into a large vessel of cold water, it forms that locity on account of the heat. The emery cylinder red powder, which is called the grenaille; they cut rather faster. But, although the friction was repeat the operation every time they in this manner made to operate successively and by frequent separate the copper; and this furnishes them with changes on the whole surface of the file, it soon as much of the grenaille as they have occasion for became too hot to be held; and, when a cloth was in their china works. used to defend the workman's hand, the work not only went on awkwardly, but the heat increased to GRIEF. The influence of this passion on the such a degree, that the oil was decomposed, and pody is very great. Its effects resemble in several emitted an empyreumatic smell. The stone was instances those of fear, with, however, some varia- then allowed to dry, and the file tried upon its face. tions, owing perhaps to its being in general of It almost instantly became blue, and very soon longer duration. Grief diminishes the bodily after redhot. Both the cylinders were then covered strength in general, and particularly the force of the with tallow, by holding the end of a candle to each heart and circulation, as appear by the frequent while turning round, and emery was sprinkled on sighs and deep respirations which attend it, which the wooden one. The file was then applied to the seem to be necessary exertions, in order to promote grind-stone while in rapid motion. At first the the passage of the blood through the lungs. It friction was hardly observable, but very soon afterdiminishes perspiration, obstructs the menstrual wards, the zone of tallow pressed by the file bedischarge, produces paleness of the skin, and de- came melted, and the stone cut very rapidly. Yet matous complaints, and scirrhus of the glandular the file was for a long time hardly heated at all; parts. It aggravates the scurvy, and the malignity | and, when at last it began to feel warm, its temperof putrid and contagious distempers; and renders ature was instantly lowered by removing it to anpeople more apt to receive the infection of them. other zone of the cylinder. When it comes on suddenly, and in a great degree, it causes palpitation of the heart, and renders the pulse irregular. Blindness, gangrene, and sudden death, have followed the excess of this sensation. Its effects of changing the color of the hair are well known. Opiates, in small doses, are good cordials in this case.

GRINDING. In Cutlery, the operation of sharpening edge-tools. This operation, as usually practised, is attended with no small inconvenience, from the production of heat by friction. The heat produced is so great, that hard tools are often softened and spoiled by the steel becoming ignited during the grinding. To prevent this effect, the grind-stone is partly immersed in a trough of water; but in this case the rotation of the stone must be moderate, and the work, of course, slow, else the water will be thrown off by the centrifugal force. When the water is applied from above by a cock, the quantity is too small to counteract the heat, and preserve the necessary low temperature. It has even been found, that the edge or point of a hard tool ground under water will be softened, if it be not held so as to meet the stream, sparks being often produced even under water.

The same effects were produced on the wooden cylinder. This is easily explained upon the modern theory of heat. When oil was used on the wooden cylinder, the heat produced by the friction was employed in raising the temperature of the file and the oil; but when tallow was used, instead of the oil, the greatest part of the heat was exhausted in melting this substance. From the increased capacity of the tallow when fused, the heat was absorbed and became latent, instead of raising the temperature: and when the melted tallow began to grow hot, together with the file, the temperature was easily reduced by employing the heat on another zone of tallow. Mr. Nicholson used these two cylinders in a considerable quantity of work with great satisfaction. This discovery bids fair to be of great utility.

GRIND-STONES. In the Manufactures, are flat circular stones used for the grinding of edgetools, when such are mounted on a spindle, and turned by a winch-handle, as is common in every part of the country; but in districts where cutlery and tools are manufactured, great numbers of these stones are used in one building, called a grind-mill or blade-mill, and are turned by water or steam

engines. The stone suited to form grind-stones is utmost extravagance of the imagination is allowed what is denominated a sharp grit, that is, the grains to revel, without regard to nature or probability. of sand or silex of which it is composed are partly uniform in size, and are firmly attached to each other by a siliceous or other very hard cement, without the interstices between the grains being filled up, as frequently is the case, or nearly so, with the other kinds of sand-stone.

A taste and style of ornament which has been employed to decorate walls, ceilings, furniture, &c. ever since the discovery of antique, monumental paintings, and sculptures in subterranean chambers near Rome, and throughout Italy, which were adorned by it in the times of the ancient Romans. Hence the name is derived, the Italians calling all such places grotte.

GRISGRIS. A superstition greatly in vogue among the negroes in the interior parts of Africa. Its origin is discernible in the Egyptian hieroThe grisgris, according to Le Maire, are certain glyphic writing, where the heads and limbs of men Arabic characters, mixed with magical figures and beasts are attached to blocks of stone, to vases, drawn by the Marabuts or priests upon paper. or to foliage, &c. thereby characterising the incliLabat affirms, that they are nothing else than scraps nations and the powers of the Deity, or person of the Alcoran in Arabic; but the words are prob- whose history they record, or whose peculiar transably of the Mandingo language, though the char-actions they are intended to preserve in the reacters are an attempt to imitate the Arabic. The membrance of future ages.

poorest negro never goes to war without his gris- With the Egyptians it remained rude and ungris, as a charm against wounds; and if it proves polished; but when the Greeks adopted it, they ineffectual, the priest transfers the blame on the made an ornamental use of it, and it became a immorality of his conduct. These priests invent medium to exhibit their general knowledge of nagrisgris against all kinds of dangers, and in favor ture. The taste with which they united in one of all desires and appetites; by virtue of which form, not only parts of various animals, but objects the possessors may obtain or avoid whatever they so totally diverse in their nature and appearance, like or dislike. No priests in the world are more as the productions of the animal and vegetable honored and revered by the people than these im- kingdoms, is in the highest degree delightful to posters are by the negroes; nor are any people in contemplate. The formation of chimerical beings, the world more impoverished by their priests than as the dragon, the sphinx, the griffin, &c. owe these negroes are, a grisgris being frequently sold their origin to this taste; which received much of at three slaves and four or five oxen. The grisgris its force and interest in heathen days, from the intended for the head is made in the form of a mythological enigmas couched under these comcross, reaching from the forehead to the neck be- pound forms. Such is the character of that ornahind, and from ear to ear; nor are the arms and ment so common on Egyptian structures, the wingshoulders neglected. Sometimes they are planted ed serpent surrounding an egg. Now, that these in their bonnets in the form of horns; at other mysterious and emblematic meanings are disretimes they are made like serpents, lizards, or some garded, and no longer treated with reverence, groother animals, out of a kind of pasteboard. tesque painting and sculpture are continued in use merely because the forms they produce are pleasing to the eye; and although the understanding is insulted by them, yet such is the power of the beauty of forms, that we are gratified by it, in spite of our reason.

GROAT. In England, a silver coin, first struck in the reign of Edward I. It has since been used as a money of account equal to four pence.

GROOVE. In Architecture, a channel cut in a piece of wood, by taking away a rectangular prism adjacent to any of its superfices, and thereby forming two internal angles and two external angles on the said piece; and hence a groove differs from a rebate in this, that the same solid is taken away in both; the part taken away in the former always leaves the surface equally prominent on both sides of the groove, whereas in the latter it it only so on one side, the arris being cut away, and has only one internal angle. Grooves are sometimes used by way of ornament and sometimes to insert the tongue of some other piece of work, and by this means fasten the part which contains the groove to the other which contains the tongue.

GROSS-BEAK. A bird with a stout bill, and of a fiery red color, except round the bill and on the throat, which is black. It is to be met with in North America, and is called the Virginia nightingale, on account of the fineness of its song.

GROTESQUE. In Painting and Sculpture, a word adopted from the French, and signifies, together with the Italian grottesca, the representation of deformed and monstrous objects, in which the

Grotesque work is at present chiefly confined in its application to monumental sculpture, where it retains somewhat of its emblematic origin; to carvings or painting of furniture, wherein beauty of ornament is principally sought for in it; and sometimes it is employed in painting and stucco on the interior of rooms, but rarely to any great extent; a better and more simple taste having in a great measure superseded it.

GROTTO. A large deep cavern or den in a mountain or rock. The word is Italian, grotta, formed from the Latin crypta. The ancient anchorites retired into dens and grottos, to apply themselves the more attentively to meditation.

The Grotto del Cane, situated about two miles from Naples, is celebrated for the noxious nature of the air contained in it, which is in fact carbonic acid gas. As this gas, from its weight, must always lie along the bottom of the cavern, small animals on entering must breathe it; whereas a man may traverse it in safety, as his head is considerably above the pestilential vapor. The height to which the gas rises may be seen from observing the color of the sides of the cavern.