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in the Planets are as their Powers at equal distances from their Centres: And, lastly, since the Weights of equal and homogeneous Bodies towards homogeneous Spheres, are, at the Surfaces of the Spheres, as the Diameters of those Spheres; and, consequently, the Densities of heterogeneous Bodies are as the Weights at the Diameters of the Spheres. See DENSITY,

VI. The common Centre of Gravity of the Sun, and all the Planets, is at rest: And the Sun, the always in Motion, yet never recedes far from the common Center of all the Planets.

For, the Matter in the Sun being to that in Jupiter as 1033 to 1; and Jupiter's distance from the Sun to the Semi-diameter of the Sun in a Ratio somewhat bigger; the common Center of Gravity of Jupiter and the Sun, will be a Point a little without the Sun's Surface. And by the fame means the common Centre of Saturn and the Sun will be a Point a little within the Sun's Surface: And the common Centre of the Earth, and all the Planets will be scarce one Diameter of the Sun distant from the Centre thereof. But the Centre is always at rest: Therefore, the the Sun will have a Motion this and that way, according to the various Situations of the Planets, yet it can never recede far from the Centre. So that the common Centre of Gravity of the Earth, Sun, and Planets may be esteem'd the Centre of the whole World. See SUN and CENTRE.

VII. The Planets move in Ellipses that have their Foci in the Centre of the Sun; and describe Areas proportional to their Times.

This we have already laid down à posteriori, as a Phenomenon And now, that the Principle of the heavenly Motions is shewn, we deduce it therefrom à priori. Thus: Since the Weights of the Planets towards the Sun are reciprocally as the Squares of their distances from the Centre of the Sun; if the Sun were at rest, and the other Planets did not act on each other; their Orbits would be Elliptical, having the Sun in their common Umbilicus; and would describe Areas proportional to the Times: But the mutual Actions of the Planets are very small, and may be well thrown afide. Therefore, &c. See PLANET and ORBIT.

Indeed, the Action of Jupiter on Saturn is of some consequence; and hence, according to the different Situations and Distances of those two Planets, their Orbits will be a little disturbed. See DISTURBING Force.

The Sun's Orbit too, is sensibly disturbed by the Action of the Moon: And the common Centre of the two describes an Ellipsis round the Sun placed in the Umbilicus; and with a Radius drawn to the Centre of the Sun, describes Areas proportional to the Times. See Earth and Saturn.

VIII. The Aphelia and Nodes of the Planets are at rest. Excepting for some inconsiderable Irregularities arising from the Actions of the revolving Planets and Comets. Consequently, as the fix'd Stars retain their Pofition to the Aphelia and Nodes; they, too, are at rest. See NODE, STAR, &c.

IX. The Axis, or Polar Diameter of the Planets, is less than the Equatorial Diameter. and by Radii drawn to the Sun, describe Areas proportional to the Times; that the Orbits, or Trajectories, are very nearly Parabolas; that their Bodies are solid, compact, &c. like those of the Planets, and must therefore acquire an immense heat in their Perihelia; that their Tails are Exhalations arising from them, and encompassing them like Atmospheres. See Comet.

The Planets, had they no diurnal Rotation, would be Spheres as having an equal Gravity on every side: But by this Rotation, the Parts receding from the Axis, endeavour to rise towards the Equator, which, if the Matter they consist of be fluid, will be affected very sensibly. Accordingly Jupiter, whose Density is found not much to exceed that of Water on our Globe, is observed by the Astronomers to be considerably less between the Poles, than from East to West. And on the same Principle, unless our Earth were higher at the Equator than towards the Poles, the Sea would rise under the Equator, and over-flow all near it. See Spheroid.

But this Figure of the Earth, Sir I. Newton proves like- wife à posteriori; from the Oscillations of Pendulums being flower, and smaller, in the Equatorial, than the Polar Parts of the Globe. See Pendulum.

X. All the Moon's Motions, and all the Inequalities in those Motions, follow from these Principles: E. gr. Her unequal Velocity, and that of her Nodes, and Apogee in the Syzygies and Quadratures; the differences in her Eccentricity, and her Variation, &c. See Moon, Quadrature, Syzygy, &c.

XI. From the Inequalities in the Lunar Motions, we can deduce the several Inequalities in the Motions of the Satellites. See Sattellites.

XII. From these Principles, particularly the Action of the Sun and Moon upon the Earth, it follows, that we must have Tides; or that the Sea must swell and subside twice every Day. See Tides.

XIII. Hence likewise follows, the whole Theory of Comets; as, that they are above the Region of the Moon, and in the Planetary Spaces; that they shine by the Sun's Light reflected from them; that they move in Conic Sections, whose Umbilici are in the Centre of the Sun: and by Radis drawn to the Sun, describe Areas proportional To the Times; that the Orbits, or Trajectories, are very nearly Parabolas; that their Bodies are solid, compact, &c. like those of the Planets, and must therefore acquire an immense heat in their Perihelia; that their Tails are Exhalations arising from them, and encompassing them like Atmospheres. See Comet.

The Objections rais'd against this Philosophy, are chiefly against the Principle Gravity; which some condemn as an occult Quality, and others as a miraculous, and præter-natural Cause; neither of which have longer any room in found Philosophy. Others, again, set it aside, as destroying the Notion of Vortices; and others, as supposing a Vacuum. But these are all abundantly obviated under the Articles GRAVITY, ATTRACTION, VORTEX, VACUUM, QUALITY, &c.

NEXUS of Matter, see Conhesion.

NICHE, in Architecture, a Cavity, or Sinking, in the Thickness of a Wall; to place a Figure, or Statue in. See Statue.

The larger Niches serve for Groups of Figures; the small ones for single Statues, sometimes only for Butts. The Word comes from the Italian Nicchio, Sea-Shell; in regard the Statue is here inclosed as in a Shell; or, perhaps, by reason of the Shell wherewith the Top of some of them is adorn'd.

Great Care must be taken to proportion the Niches to the Figures; and that the Pedestals of the Figures be proportion'd to the Niches.

Round Niche, is that whose Plan and Circumference are Circular.

Square Niche, That where they are Square.

Angular NICHE, That form'd in a Corner of the Building.

Ground NICHE, That which, instead of bearing on a Massive, has its Rise from the Ground; as the Niches of the Portico of the Pantheon at Rome: These are otherwise call'd Tribunals. See TRIBUNAL.

Niches are sometimes made with Rustic-work, sometimes with Shell-work, and sometimes of Crail'd, or Arbor-work.

NICHOLAITANS, or NICOLAITANS, one of the most antient Sects in the Christian Church. It had its Name from Nicholas, a Person ordain'd a Deacon of the Church of Jerusalem together with St. Stephen.

The distinguishing Tenet of the Nicholaitans, as repre- sented by Ecclesiaftical Historians, is, that all Married Women should be common; to take away all occasion of Jealousy.

Other Authors tax Nicholas with other Impurities; but Clemens Alexandrinus imputes them all to his Disciples, who, he says, abused their Master's Words. Nicholas, it seems, having a very beautiful Wife, was suspected by the Apostles as jealous of her, and as being a lafcivious Man.

To remove this suspicion, he call'd his Wife; and to shew he was not at all attach'd to her, offer'd any of them the liberty of espoufing her. This is confirm'd by Eusebius, who adds, that Nicholas never had more than one Wife.

Other things charg'd on the Nicholaitans, are, That they made no scruple of eating Meats offer'd to Idols: That they maintain'd that the Father of Jesus Christ was not the Creator: That some of them adored one Barbelo, who inhabited the eighth Heaven, and who proceeded from the Father, and was the Mother of Jaldabaoth; or, according to others, of Sabaoth, who had forcibly taken possession of the seventh Heaven. Others of them gave the Name Prounicos to the Mother of the heavenly Powers; but all ascribe infamous Actions to her, and with her authorize their own Impurities. Others shewed Books, and pretended Revelations under the Name of Jaldabaoth.

Irenæus and Epiphanius relate thefe and other Extravagancies; and represent the Nicholaitans as Authors of the Sect of Gnostics. See Gnostics.

Cocceius, Hoffman, Vitringa, and Mains, take the Name Nicholaitan to be coin'd, to signify a Man addicted to Pleasure and Debauchery; adding, that it has nothing to do with Nicholas one of the seven Deacons. And, as the Doctrine of the Nicholaitans is mention'd in the Apocalypse, immediately after mention made of Balaam, and his Doctrine, they compare the two Names Balaam and Nicholas, which, in their Originals, the one in Greek, the other Hebrew, have nearly the same signification, viz. Prince, or Master of the People.

Mains adds, 'twas probable enough the Nicholaitans might value themselves on being the Disciples of one of the seven Deacons; but that it was without any ground: notwithstanding what the Antients, ever too credulous, have represented to the contrary.

NICOTIANA, or Herba Nicotiana, a Term given to Tobacco; from Nicot the French Ambassador at the Court of Portugal, who first sent it into France in 1560, and gave ithis