they are used in Ireland, and in the Highlands of Scotland, to dye a dark brown or ches. nut 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 Polygamia Dioecia class and order. Natural order of Holoraceæ. Elæagmi, Jussieu. Essential character: calyx, five parted; co-. rolla none: male, stamens ten: hermaphrodite, 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 of 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 Missisippi, where it abounds, and is called the olive tree. or o, the fourteenth letter, and 0, 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 used for eleven; and with a dash over it, thus O, for eleven thousand. In music, the O, or rather a circle, or double CƆ, 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. 0. 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 objectglass, and the other half that diameter; divide the smaller circumference 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 regularity 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, OAT. See AVENA. at several distant objects; for that objectOBELISK, in architecture, a truncated, glass is always the best which represents OAKUM, old ropes untwisted, and pull ed 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 consequently moving the vessel, by rowing. 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 observing, 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 PER SPECTIVE. 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 axis 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. 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 an 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 ele vated 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, Jussien. Essential character: calyx twoleaved; corolla four-cleft, bell-shaped; stamina from the slits of the corolla; capsule one-celled, two-valved, many-seeded. There is but one species, riz. 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 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 continned 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 Flamsteed; a man who, as Dr. Halley expresses it, seemed born for the employment. During fourteen years he watched the motions of the planets with upwearied 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 1630, 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 tak ing 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 Cœlestis Britannica, published in 1725; the principal part of which is the Britannic Catalogue of the fixed stars. Mr. Flamsteed, on his death in 1719, was succeeded by Dr. Halley, and he by Dr. Bradley in 1742, and this last by Mr. Bliss in 1762; but none of the observations 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 die 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 land-locked 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 magnificient 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 exceed. ingly large; but the divisions are less accurate, and, in some respects, the contrivance is less commodious than in those of the Europeans. The chief are, an armillary zodiacal sphere of six Paris feet diameter, an azimuthal horizon six feet diameter, a large quadrant six feet radius, a sextant eight feet radius, and a celestial globe six diameter. East Indies, which is still one of the princiBramin's Observatory at Benares, in the the original Gentoos of Hindostan. This pal seminaries of the Bramins, or priests of observatory at Benares it is said was built about 200 years since, by order of the Emperor Ackbar: for as this wise prince endeavoured to improve the arts, so he wished also to recover the sciences of Hindostan, and therefore ordered that three such place; |