a curious machine for representing the motions or phases of the heavenly bodies. See ASTRO-NOMY, p. 317.

It would be too great an undertaking here to give an account of the mechanism of the larger sort of orreries, which represent the movements of all the heavenly bodies; nor indeed can it be done either by diagram or description, to render it intelligible to the most discerning reader: but, instead of that, we shall exhibit an idea of the theory and structure of an useful, concise, and portable planetarium, which any gentleman may have made for a small expense, and will exhibit, very justly, the motions of all the primary planets about the sun, by wheel-work; and those that have secondaries, or moons, may have them placed about their primaries moveable by the hand, so that the whole shall be a just representation of the solar system, or true state of the heavens, for any given time of the year. In order to this we must compare, and find out the proportion, which the periodical times, or revolutions of the primary planets, bear to that of the earth: And they are such as are expressed in the table below, where the first column is the time of the earth's period in days and decimal parts; the second, that of the planets; the third and fourth are numbers in the same proportion to each other: as,

\[ \begin{align*} 36525 : 88 & \quad \text{for Mercury.} \\ 36525 : 2247 & \quad \text{for Venus.} \\ 36525 : 6869 & \quad \text{for Mars.} \\ 36525 : 433245 & \quad \text{for Jupiter.} \\ 36525 : 107593 & \quad \text{for Saturn.} \end{align*} \]

If we now suppose a spindle or arbour with six wheels fixed upon it in an horizontal position, having the number of teeth in each, corresponding to the numbers in the third column, viz. the wheel AM of 83 teeth, BL of 52, CK of 50 (for the earth), DI of 40, EH of 7, and FG of 5; and another set of wheels moving freely about an arbor, having the number of teeth in the fourth column, viz. AN of 20, BO of 32, CP of 50 (for the earth), DQ of 75, ER of 83, and FS of 148; then, if those two arbors of fixed and moveable wheels are made of the size, and fixed at the distance from each other, as here represented in the scheme, the teeth of the former will take those of the latter, and turn them very freely when the machine is in motion.

These arbors, with their wheel, are to be placed in a box, of an adequate size, in a perpendicular position: the arbor of fixed wheels to move in pivots at the top and bottom of the box; and the arbor of moveable wheels to go thro' the top of the box, to a proper height, on the top of which is to be placed a round ball, gilt with gold to represent the sun. On each of the moveable wheels is to be fixed a socket, or tube, ascending above the top of the box, and having on the top a wire fixed, and bent at a proper distance into a right angle upwards, bearing on the top a small round ball, representing its proper planets.

If then on the lower part of the arbor of fixed wheels be placed a pinion of screw-teeth, a winch turning a spindle with an endless screw, playing in the teeth of the arbor, will turn it with all its wheels; and these wheels will move the others about, with their planets, in their proper and respective periods of time, very exactly. For while the fixed wheel CK moves its equal CP once round, the wheel AM will move AN a little more than four times round, and so will nicely exhibit the motion of Mercury; and the wheel FG will turn the wheel FS about \(\frac{1}{29.5}\) round, and so will truly represent the motion of Saturn: and the same is to be observed of all the rest.

**Orrery (Earl's of).** See Boyle.

**Orrice.** See Iris.

**Orsato (Sertorio),** a celebrated antiquarian, historian, and poet, was born at Padua, in 1617, and early discovered a taste for literature and the sciences. He applied himself to searching out antiquities and ancient inscriptions; for which purpose he travelled through all the different parts of Italy, and in the mean time poetry was his amusement. When advanced in age, he taught natural philosophy in the university of Padua. He was also a member of the academy of the Ricovrati. Having presented to the doge and senate of Venice, the history of Padua, which he had dedicated to them, he made a long speech, during which he struggled with a natural want, and died of suppression of urine, on the 3rd of July 1678. He wrote a great number of books which are esteemed, some in Latin, and others in Italian.

He ought not to be confounded with John Baptist Orsato, an able physician and antiquary, who was born at Padua, in 1673, and wrote, 1. *Dissertatio epistolaris de Lucernis antiquis.* 2. A dissertation De paterna antiquorum. 3. A small treatise De ferrinis veterum; and some other works.

**ORSI (John Joseph),** an ingenious philologer and poet, was born at Bologna in the year 1652; and studied polite literature, philosophy, the civil law, and mathematics. His house was a kind of academy, where many persons of literature regularly assembled. He wrote many ingenious sonnets, pastorals, and other works in Italian, and died in 1733.

**Ortegal cape,** the most northern promontory of Spain, where there is also a castle of the same name. W. Long. 8. 20. N. Lat. 44. 0.

**Ortelius' (Abraham),** a celebrated geographer, born at Antwerp, in 1527, was well skilled in the languages and the mathematics; and acquired such reputation by his skill in geography, that he was named the Ptolemy of his time. Julius Lipfus, and most of the great men of the 16th century, were Ortelius's friends. He resided at Oxford, in the reign of Edward VI. and came a second time into England, in 1577. His *Theatrum Orbis* was the completest work of the kind that had ever been published, and gained him a reputation equal to his immense labour in compiling it. He also wrote several other excellent geographical works; the principal of which are his *Thesaurus,* and his *Synoima Geographica.* The world is likewise obliged to him for the *Britannia,* which he persuaded Camden to undertake. He died at Antwerp, in 1598.

**Orthodox,** in church-history, an appellation given to those who are found in all the articles of the Christian faith.

**Orthographic projection of the Sphere,** that wherein the eye is supposed to be at an infinite distance; so called, because the perpendiculars from any point of the sphere will all fall in the common intersection of the sphere with the plane of the projection. See Geography, no 13. 41. and Projection.

**Orthography,** that part of grammar which teaches the nature and affections of letters, and the just method of spelling or writing words, with all the proper and necessary letters; making one of the four greatest divisions or branches of grammar. See Grammar.

**Orthography,** in geometry, the art of drawing or delineating the fore-right plan of any object, and of expressing the heights or elevations of each part. It is called Orthography, for its determining things by perpendicular lines falling on the geometrical plane.

**Orthography,** in architecture, the elevation of a building.

**Orthography,** in perspective, is the fore-right side of any plane, i.e. the side or plane that lies parallel to a straight line, that may be imagined to pass through