Dom. Let.

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NUMBER, in Grammar, a modification of nouns, verbs, &c. to accommodate them to the varieties in their objects, considered with regard to number. See GRAMMAR.

NUMBERS, in poetry, oratory, music, &c. are certain measures, proportions, or cadences, which render a verse, period, or song, agreeable to the ear.

NUMERAL letters, those letters of the alphabet which are generally used for figures, as I, V, X, L, C, D, M.

NUMERATION, or notation, the art of expressing in characters any number proposed in words; or of expressing in words any number proposed in characters. See ARITHMETIC; NOTATION.

NUMERICAL, or NUMERAL, Something belonging to numbers; as numerical algebra is that which makes use of numbers instead of letters of the alphabet, also, numerical difference is the difference whereby one individual is distinguished from another. Hence a thing is said to be numerically the same, when it is so in the strictest sense of the word.

NUMIDIA, the PINTADO, or guineahen, in natural history, a genus of birds of the order Gallinæ. Generic character: bill strong and short, with a carunculate cere at the base, in which the nostrils are lodged; head horned, with a compressed coloured callus; wattles hanging from the cheeks; tail short, and pointing downwards; body speckled. There are

four species. N. meleagris, is of the size of a very large fowl, and is the meleagris of the ancients, who used to prize it as a high delicacy. Its native territory is Africa, and particularly, perhaps, Nubia. It is gregarious, having been often seen in very numerous flocks. It is now extremely common in this country. The female lays many eggs, and, secreting her nest, sometimes will suddenly appear with a family of twenty young ones. It is a bird of harsh sound, and almost perpetually uttering it. The flesh of the young birds is valued, and its eggs are thought preferable to those of the common hen. See Aves, Plate X. fig. 5.

He

NUNEZ (PERO), in biography, one of the ablest mathematicians of his time, born at Alcaza do Sal, in Portugal. taught publicly in the university of Coimbra, and instructed the Infante de Luis so well, that it is said he fitted him for a professor. Pero Nunez is well known, in the history of science, as the person who made the first improvement in the method of reading an observed angle, and the scale which he invented for this purpose, though it has received some improvements, is still called the Nonius, his latinized name. His works

are numerous.

NUT-galls are excrescences formed on leaves of the oak by the puncture of an insect, which deposits an egg in them. The best are known by the name of Aleppo-galls, imported very largely into this country for the use of dyers, calico-printers, &c. These are hard like wood, of a bluish colour, and of a disagreeable taste. They are partly soluble in water, and what remains is tasteless, and possesses the properties of the fibre of wood. By experiments Mr. Davy found that 500 grains of Aleppo-galls formed with water a solu.

NUTATION, in astronomy, a kind of tremulous motion of the axis of the earth, whereby, in each annual revolution, it is twice inclined to the ecliptic, and as often returns to its former position.

Sir Isaac Newton observes, that the moon has the like motion, only very small, and scarcely sensible.

NUTMEG, in natural history, the kernel of a large fruit, not unlike the peach, the produce of a tree called, by botanists, MYRISTICA, which see.

The nutmeg is separated from its investient coat, the mace, before it is sent over to us; except that the whole fruit is sometimes imported in preserve, by way of sweetmeat, or as a curiosity. See MACE.

The nutmeg, as we receive it, is of a roundish or oval figure, of a tolerably compact and firm texture, but easily cut with a knife, and falling to pieces on a smart blow. Its surface is not smooth, but furrowed with a number of wrinkles, running in various directions, though principally longitudinally. It is of a greyish brown colour on the outside, and of a beautiful variegated hue within, being marbled with brown and yellow variegations, running in perfect irregularity through the whole substance. It is very unctuous and fatty to the touch, when powdered, and is of an extremely agreeable smell, and of an aromatic taste, with out the heat that attends that kind of flavour in most of the other spices.

There are two kinds of nutmeg in the shops, the one called by authors the male, and the other the female. The female is the kind in common use, and is of the shape of an olive; the male is long and cylindric, and has less of the fine aromatic flavour than the other, so that it is much less esteemed, and people who trade largely in nutmegs will seldom buy it. Besides this oblong kind of nutmegs, we sometimes meet with others of perfectly irregular figures, but mere lusus naturæ, not owing to a different species of the

tree. The longer male nutmeg, as we term it, is called by the Dutch the wild nutmeg. It is always distinguishable from the others, as well by its want of fragrancy, as by its shape it is very subject to be worm-eaten, and is strictly forbid, by the Dutch, to be packed up among the other, because it will give occasion to their being worm-eaten by the insects getting from it into them, and breeding in all parts of the parcel. The largest, heaviest, and most unctuous of the nutmegs are to be chosen, such as are the shape of an olive, and of the most fragrant smell.

NUTRITION. See PHYSIOLOGY.

NYCTANTHES, in botany, a genus of the Diandria Monogynia class and order. Natural order of Sepiariæ. Jasmineæ, Jussieu. Essential character: corolla, salver-shaped, with truncated segments; capsule, two-celled, margined; seeds solitary. There are seven species, of which N. undulata, wave-leaved Nyctanthes, is a shrub about six feet in height; the young shoots are hairy; leaves of a shining green, smooth, in pairs from the joints, bitter, without any smell; flowers white; calycine segments six; of the corolla, six, seven, or eight, narrow, much waved on the edge; fruit superior, resembling a black cherry, containing a round hairy seed. It is a native of the East Indies, where it is much cultivated on account of the sweetness of the flowers, which are worn by the ladies in their hair.

NYMPH, or PUPA, among naturalists, the state of winged-insects between their living in the form of a worm, and their appearing in the winged or most perfect

state.

The eggs of insects are first hatched into a kind of worms, or maggots; which afterwards pass into the nymph-state, surrounded with shells or cases of their own skins; so that, in reality, these nymphs are only the embryo-insects wrapped up in this covering; from whence they at last get loose, though not without great difficulty.

Linnæus applied the term Pupa to this state of the insect, from a fancied resemblance which it bears to a child wrapped in swaddling clothes, according to the old European fashion.

NYMPHÆ. See ANATOMY.

NYMPHEA, in botany, water-lily, a genus of the Polyandria Monogynia class and order. Natural order of Succulenta. Hydrocharides, Jussieu. Essential character, calyx four, five, or six-leaved; co

rolla many-petalled; berry many celled, truncated. There are six species, of which N. alba, white water-lily, has a tuberous root, creeping far and wide in the mud; the whole plant is larger than the yellow water-lily; petioles and peduncles round, within full of pores; flowers large and very handsome; petals white, from sixteen to twenty in number; stamens sixty-eight or seventy; germ roundish; style none; stigma rayed; according to Linnæus, the flower raises itself out of the water and expands about seven o'clock in the morning, closing again, and reposing upon the surface of the water soon after four in the evening.

The roots have an astringent bitter taste; they are used in Ireland, and in the Highlands of Scotland, to dye a dark brown or chesnut colour; this plant is a native of most parts of Europe, in slow streams, pools and ditches, flowering in July and August.

NYSSA, in botany, a genus of the Poly gamia Dioecia class and order. Natural order of Holoraceæ. Elæagmi, Jussieu. Essential character: calyx, five parted; corolla none: male, stamens ten: herma

phrodite, stamens five; pistil one; drupe inferior. There are two species, viz. N. integrifolia, mountain tupelo; and N. denticulata, water tupelo: the former of which grows naturally in Pennsylvania, rising to the height of thirty or forty feet, and nearly two in diameter, sending off many horizontal and often depending branches; leaves a dark green colour on the upper surface, but lighter underneath; the flowers are produced upon long footstalks, from the base of the young shoots, dividing irregularly into several parts, each supporting a small flower; the female trees have fewer flowers, produced upon much longer simple cylindrical footstalks. The Virginian water tupelo tree grows naturally in wet swamps, or near large rivers in Carolina and Florida, rising with a strong upright trunk to the height of eighty or an hundred feet, dividing into many branches towards the top; the leaves are large, of an oval spear-shaped form; the berries are nearly the size and shape of small olives, and are preserved by the French inhabitants upon the Mississippi, where it abounds, and is called the olive tree.

or o, the fourteenth letter, and fourth vowel of our alphabet, pronounced as in the words nose, rose, &c.

The sound of this letter is often so soft as to require it double, and that chiefly in the middle of words; as goose, reproof, &c. and in some words this oo is pronounced like u short, as in flood, blood, &c.

As a numeral, O is sometimes use for eleven; and with a dash over it thus, O, for eleven thousand.

In music, the O, or rather a circle, or double Co, is a note of time, called by us a semi-breve; and by the Italians, circolo. The O is also used as a mark of triple time, as being the most perfect of all figures. See TRIPLE.

OAK. See QUERCUS.

OAKUM, old ropes untwisted, and pulled out into loose hemp, in order to be used in caulking the seams, tree nails, and bends of a ship, for stopping or preventing leaks.

OAR, in navigation, a long piece of wood, made round where it is to be held in the hand, and thin and broad at the other end, for the easier cutting and resisting the water, and conseqnently moving the vessel, by rowing.

OAT. See AVENA.

OBELISK, in architecture, a truncated, quadrangular, and slender pyramid, raised as an ornament, and frequently charged either with inscriptions or hieroglyphics.

OBJECT, in philosophy, something apprehended, or presented to the mind, by sensation or by imagination.

OBJECT glass of a telescope, or microscope, the glass placed at the end of the tube which is next the object.

To prove the goodness and regularity of an object-glass, on a paper describe two concentric circles, the one having its diameter the same with the breadth of the object glass, and the other half that diameter; divide the smaller circumfer

ence into six equal parts, pricking the points of division through with a fine needle; cover one side of the glass with this paper, and, exposing it to the sun, receive the rays through these six holes upon a plane; then by moving the plane nearer to, or further from the glass, it will be found whether the six rays unite exactly together at any distance from the glass; if they do, it is a proof of the regu larity and just form of the glass; and the said distance is also the focal distance of the glass. A good way of proving the excellency of an object-glass is, by placing it in a tube, and trying it with small eye-glasses, at several distant objects; for that object-glass is always the best, which represents objects the brightest and most distinct, and which bears the greatest aperture, and the most convex and concave eye-glasses, without colouring or haziness. A circular object-glass is said to be truly centered, when the centre of its circumference falls exactly in the axis of the glass; and to be ill centered, when it falls out of the axis. To prove whether object-glasses be well centered, hold the glass at a due distance from the eye, and observe the two reflected images of a candle, varying the distance till the two images unite, which is the true centre point: then if this fall in the middle, or central point of the glass, it is known to be truly centered. As object-glasses are commonly included in cells that screw upon the end of the tube of a telescope, it may be proved whether they be well centered, by fixing the tube, and observ ing, while the cell is unscrewed, whether the cross-hairs keep fixed upon the same lines of an object seen through the telescope.

OBJECTIVE line, in perspective, is any line drawn on the geometrical plane, whose representation is sought for in a draught or picture: and the objective plane is any plane situated in the horizontal plane, the representation of which is required. See PERSPECTIVE.

OBLATE, flattened, or shortened, as an oblate spheroid, having its axis shorter than its middle diameter, being formed by the rotation of an ellipse about the shorter axis. The oblateness of the earth refers to the diminution of the polar axis in respect of the equatorial. The ratio

of these two axes has been determined in various ways; sometimes by the measures of different degrees of latitude, and sometimes by the length of pendulums, vibrating seconds in different latitudes. See EARTH, Degree, &C.

VOL. IX.

OBLIGATION, in law, a bond containing a penalty, with a condition annexed, either for payment of money, performance of covenants, or the like. This security is called a specialty. See BOND and DEED.

OBLIGOR, in law, he who enters into an obligation; as obligee is the person to whom it is entered into.

OBLIQUE, in geometry, something aslant, or that deviates from the perpendicular. Thus an oblique angle is either an acute or obtuse one, i. e. any angle except a right one. See ANGLE.

OBLIQUE cases, in grammar, are all the cases except the nominative.

OBLIQUE line, that which, falling on another line, makes oblique angles with it, viz. one acute, and the other obtuse.

OBLIQUE planes, in dialling, are those which recline from the zenith, or incline towards the horizon.

The obliquity, or quantity of this inclination, or reclination, may be found by means of a quadrant.

OBLIQUE sailing, in navigation, is when a ship sails upon some rhumb between the four cardinal points, making an oblique angle with the meridian; in which case she continually changes both latitude and longitude. Oblique sailing is of three kinds, viz. plain sailing, Mercator's sailing, and great circle sailing. See NAVIGATION.

OBLIQUE sphere, is where the pole is elevated any number of degrees less than 90°: in which case the axis of the world, the equator, and parallels of declination, will cut the horizon obliquely.

OBLIQUITY of the ecliptic. See ECLIP

TIC.

OBLIQUUS, in anatomy, oblique, a name given to several muscles, particularly in the head, eyes, and abdomen. See ANATOMY.

OBOLARIA, in botany, a genus of the Didynamia Angiospermia class and order. Natural order of Personatæ. Pediculares, Jussieu. Essential character: calyx twoleaved; corolla four-cleft, bell-shaped; stamina, from the slits of the corolla; capsule one-celled, two-valved, manyseeded. There is but one species, viz. O. Virginica.

OBSERVATION, in astronomy and navigation, is the observing with an instrument some celestial phenomenon, as the altitude of the sun, moon, and stars, or their distances from each other. But by this term, mariners commonly mean only the taking the meridian altitudes, in order to find the latitude; and the finding

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the latitude from such observed latitude, they call "working an observation."

OBSERVATORY, a place destined for observing the heavenly bodies; it is a building usually in form of a tower, erected on an eminence, and covered with a terrace for making astronomical observations. Most nations have had observatories, which have been noticed at large in La Lande's Astronomy: of these, the following may be mentioned:

The Greenwich Observatory, or Royal Observatory of England. This was built and endowed in the year 1676, by order of King Charles the Second, at the instance of Sir Jonas Moore and Sir Christopher Wren; the former of these gentlemen being Surveyor General of the Ordnance, the office of Astronomer Royal was placed under that department, in which it has continued ever since.

This observatory was at first furnished with several very accurate instruments; particularly a noble sextant of seven feet radius, with telescopic sights. And the first Astronomer Royal, or the person to whom the province of observing was first committed, was Mr. John Flamstead; a man who, as Dr. Halley expresses it, seemed born for the employment. During fourteen years he watched the motions of the planets with unwearied diligence, especially those of the moon, as was given him in charge, that a new theory of that planet being found, shewing all her irregularities, the longitude might thence be determined. In the year 1690, having provided himself with a mural arch of near seven feet radius, made by his assistant, Mr. Abraham Sharp, and fixed in the plane of the meridian, he began to verify his catalogue of the fixed stars, which had hitherto depended altogether on the distances measured with the sextant, after a new and very different manner, viz. by taking the meridian altitudes, and the moments of culmination, or, in other words, the right ascension and declination. And he was so well pleased with this instrument, that he discontinued almost entirely the use of the sextant. Thus, in the space of upwards of forty years, the Astronomer Royal collected an immense number of good observations; which may be found in his "Historia Colestis Britannica," published in 1725; the principal part of which is the Britannic Catalogue of the fixed stars.

Mr. Flamstead, on his death in 1719, was succeeded by Dr. Halley, and he by Dr. Bradley in 1742, and this last by Mr. 'iss in 1762; but none of the observa

tions of these gentlemen have yet been given to the public.

On the demise of Mr. Bliss, in 1765, he was succeeded by Dr. Nevil Maskelyne, the present Astronomer Royal, whose valuable observations have been published, from time to time, under the direction of the Royal Society, in several folio volumes.

The Greenwich Observatory is found, by very accurate observations, to lie in 51° 28′ 40′′ north latitude, as settled by Dr. Maskelyne, from many of his own observations, as well as those of Dr. Bradley.

The Paris Observatory was built by Louis the Fourteenth, in the Fauxbourg St. Jaques; being begun in 1664, and finished in 1672. It is a singular, but magnificent building, of eighty feet in height, with a terrace at top; and here M. de la Hire, M. Cassini, &c. the King's Astronomers, have made their observations. Its latitude is 48° 50′ 14′′ north, and its longitude 9′ 20′′ east of Greenwich Observatory."

In the Observatory of Paris is a cave, or pit, 170 feet deep, with subterraneous passages, for experiments that are to be made out of the reach of the sun, especially such as relate to congelations, refrigerations, &c. In this cave there is an old thermometer of M. de la Hire, which stands at all times at the same height; thereby shewing that the temperature of the place remains always the same. From the top of the platform to the bottom of the cave is a perpendicular well or pit, used formerly for experiments on the fall of bodies; being also a kind of long telescopical tube, through which the stars are seen at mid-day.

Tycho Brahe's Observatory was in the little island Ween, or the Scarlet Island, between the coasts of Schonen and Zealand, in the Baltic Sea. This observatory was not well situated for some kinds of observations, particularly the risings and settings; as it lay too low, and was landlocked on all the points of the compass except three; and the land horizon being very rugged and uneven.

Pekin Observatory. Father le Compte describes a very magnificent observatory, erected and furnished by the late Emperor of China, in his capital, at the intercession of some Jesuit missionaries, chiefly Father Verbest, whom he appointed his chief observer. The instruments here are exceedingly large; but the divisions are less accurate; and, in some respects, the contrivance is less commodious than