Astronomy Explained Upon Sir Isaac Newton's Principles / And made easy to those who have not studied mathematics

by James Ferguson

The numeral Figures refer to the Articles, and the small n to the Notes on the Articles.

• A.
• Acceleration of the Stars, [221].
• Angle, what, [185].
• Annual Parallax of the Stars, [196].
• Anomaly, what, [239].
• Antients, their superstitious notions of Eclipses, [329].
  • Their method of dividing the Zodiac, [398].
• Antipodes, what, [122].
• Apsides, line of, [238].
• Archimedes, his ideal Problem for moving the Earth, [159].
• Areas described by the Planets, equal in times, [153].
• Astronomy, the great advantages arising from it both in our religious and civil concerns, [1] Discovers the laws by which the Planets move, and are retained in their Orbits, [2]
• Atmosphere, the higher the thinner, [174].
  • It’s prodigious expansion, ib.
  • It’s whole weight on the Earth, [175].
  • Generally thought to be heaviest when it is lightest, [176].
  • Without it the Heavens would appear dark in the day-time, [177].
  • Is the cause of twilight, ib.
  • It’s height, ib.
  • Refracts the Sun’s rays, [178].
  • Causeth the Sun and Moon to appear above the Horizon when they are really below it, ib.
  • Foggy, deceives us in the bulk and distance of objects, [185].
• Attraction, [101-105].
  • Decreases as the square of the distance increases, [106].
  • Greater in the larger than in the smaller Planets, [158].
  • Greater in the Sun than in all the Planets if put together, ib.
• Axes of the Planets, what, [19].
  • Their different positions with respect to one another, [120].
• Axis of the Earth, it’s parallelism, [302].
  • It’s position variable as seen from the Sun or Moon, [338].
    • the Phenomena thence arising, [340].
• B.
• Bodies, on the Earth, lose of their weight the nearer they are to the Equator, [117].
  • How they might lose all their weight, [118],
  • How they become visible, [167].
• C.
• Calculator, (an Instrument) described, [436].
• Calendar, how to inscribe the Golden Numbers rightly in it for shewing the days of New Moons, [423].
• Cannon-Ball, it’s swiftness, [89].
  • In what times it would fly from the Sun to the different Planets and fixed Stars, ib.
• Cassini, his account of a double Star eclipsed by the Moon, [58].
  • His Diagrams of the Paths of the Planets, [138].
• Catalogue of the Eclipses, [327].
  • Of the Constellations and Stars, [367].
  • Of remarkable Æras and events, [433].
• Celestial Globe improved, [438].
• Centripetal and centrifugal forces, how they alternately overcome each other in the motions of the Planets, [152-154].
• Changes in the Heavens, [403].
• Chords, line of, how to make, [369].
• Circles, of perpetual Apparition and Occultation, [128].
  • Of the Sphere, [198].
  • Contain 360 Degrees whether they be great or small, [207].
• Civil Year, what, [411].
• Columbus (Christopher) his story concerning an Eclipse, [330].
• Clocks and Watches, an easy method of knowing whether they go true or false, [223].
  • Why they seldom agree with the Sun if they go true, [228-245].
  • How to regulate them by Equation Tables and a Meridian line, [225], [226].
• Cloudy Stars, [402].
• Cometarium (an Instrument) described, [437].
• Constellations, antient, their number, [396].
  • The number of Stars in each, according to different Astronomers, [399].
• Cycle, Solar, Lunar, and Romish, [420].
  • Of Easter, [425].
• D.
• Darkness at our Saviour’s crucifixion supernatural, [352], [432].
• Day, natural and artificial, what, [417].
  • And Night, always equally long at the Equator, [126].
  • Natural, not compleated in an absolute turn of the Earth on it’s Axis, [222].
• Degree, what, [207].
• Digit, what, [321], n.
• Direction, (Number of) [426].
• Distances of the Planets from the Sun, an idea thereof, [89].
  • A Table thereof, [98].
  • How found, [190].
• Diurnal and annual Motions of the Earth illustrated, [200], [202].
• Dominical Letter, [427].
• Double projectile force, a balance to a Quadruple Power of Gravity, [153].
  • Star covered by the Moon, [58].
• E.
• Earth, it’s bulk but a point as seen from the Sun, [3] It’s Diameter, annual Period, and Distance from the Sun, [47].
  • Turns round it’s Axis, ib.
  • Velocity of it’s equatoreal Parts, ib.
  • Velocity in it’s annual Orbit, ib.
  • Inclination of it’s Axis, [48].
  • Proof of it’s being globular, or nearly so, [49], [314].
  • Measurement of it’s surface, [50], [51].
  • Difference between it’s Equatoreal and Polar Diameters, [76].
  • It’s motion round the Sun demonstrated by gravity, [108], [111].
    • by Dr. Bradley’s observations, [113].
    • by the Eclipses of Jupiter’s Satellites, [219].
  • It’s diurnal motion highly probable from the absurdity that must follow upon supposing it not to move, [111]. [120].
    • and demonstrable from it’s figure, [116].
    • this motion cannot be felt, [119].
  • Objections against it’s motion answered, [112], [121].
  • It has no such thing as an upper or under side, [122].
    • in what case it might, [123].
  • The swiftness of it’s motion in it’s Orbit compared with the velocity of light, [197].
  • It’s diurnal and annual motions illustrated by an easy experiment, [200].
  • Proved to be less than the Sun and bigger than the Moon, [315].
• Easter Cycle, [425].
• Eclipsareon (an Instrument) described, [442].
• Eclipses, of Jupiter’s Satellites, how the Longitude is found by them, [207-218].
  • • they demonstrate the velocity of light, [216].
  • Of the Sun and Moon, [312-327].
  • Why they happen not in every month, [316].
  • When they must be, [317].
  • Their limits, ib.
  • Their Period, [320], [326].
  • A dissertation on their progress, [321-324].
  • A large catalogue of them, [327].
  • Historical ones, [328].
  • More of the Sun than of the Moon, and why, [331].
  • The proper Elements for their calculation and projection, [353-390].
• Ecliptic, it’s Signs, their names and characters, [91].
  • Makes different Angles with the Horizon every hour and minute, [275].
    • how these Angles may be estimated by the position of the Moon’s horns, [260].
  • It’s obliquity to the Equator less now than it was formerly, [405].
  • How it’s Signs are numbered, [354].
• Elongations, of the Planets, as seen by an observer at rest on the outside of all their Orbits, [133].
  • Of Mercury and Venus as seen from the Earth, illustrated, [142].
    • it’s quantity, [143].
  • Of Mercury, Venus, the Earth, Mars, and Jupiter; it’s quantity as seen from Saturn, [147].
• Epochas or Æras, [433].
• Equation of time, [224-245].
  • Of the Moon’s Place, [355].
  • Of the Sun’s Place, ib.
  • Of the Nodes, [363].
• Equator, day and night always equal there, [126].
  • Makes always the same Angle with the Horizon of the same place; the Ecliptic not, [274], [275].
• Equinoctial Points in the Heavens, their precession, [246],
  • a very different thing from the recession or anticipation of the Equinoxes on Earth, the one no ways occasioned by the other, [249].
• Excentricities of the Planets Orbits, [155].
• F.
• Fallacies in judging of the bulk of objects by their apparent distance, [185];
  • applied to the solution of the horizontal Moon, [187].
• First Meridian, what, [207].
• Fixed Stars, why they appear of less magnitude when viewed through a telescope than by the bare eye, [391].
  • Their number, [392].
  • Their division into different Classes and Constellations, [395-399].
• G.
• General Phenomena of a superior Planet as seen from an inferior, [149].
• Gravity, demonstrable, [101-104].
  • Keeps all bodies on the Earth to it’s surface, or brings them back when thrown upward; and constitutes their weight, [101], [122].
  • Retains all the Planets in their Orbits, [103].
  • Decreases as the square of the distance increases, [106].
  • Proves the Earth’s annual motion, [108].
  • Demonstrated to be greater in the larger Planets than in the smaller; and stronger in the Sun than in all the Planets together, [158].
  • Hard to understand what it is, [160].
  • Acts every moment, [162].
• Globe, improved celestial, [438].
• Great Year, [251].
• H.
• Harmony of the celestial motions, [111].
• Harvest-Moon, [273-293].
  • None at the Equator, [273].
  • Remarkable at the Polar Circles, [285].
  • In what years most and least advantageous, [292].
• Heat, decreases as the square of the distance from the Sun increases, [169].
  • Why not greatest when the Earth is nearest the Sun, [205].
  • Why greater about three o’Clock in the afternoon than when the Sun is on the Meridian, [300].
• Heavens, seem to turn round with different velocities as seen from the different Planets; and on different Axes as seen from most of them, [120].
  • Only one Hemisphere of them seen at once from any one Planet’s surface, [125].
  • The Sun’s Center the only point from which their true Motions could be seen, [135].
  • Changes in them, [403].
• Horizon, what, [125], n.
• Horizontal-Moon explained, [187].
• Horizontal Parallax, of the Moon, [190];
  • of the Sun, [191];
  • best observed at the Equator, [193].
• Hour-Circles, what, [208].
• Hour of time equal to 15 degrees of motion, ib.
  • How divided by the Jews, Chaldeans, and Arabians, [419].
• Huygenius, his thoughts concerning the distance of some Stars, [5]
• I. J.
• Inclination of Venus’s Axis, [29].
  • Of the Earth’s, [48].
  • Of the Axis or Orbit of a Planet only relative, [201].
• Inhabitants of the Earth (or any other Planet) stand on opposite sides with their feet toward one another, yet each thinks himself on the upper side, [122].
• Julian Period, [430].
• Jupiter, it’s distance, diameter, diurnal and annual revolutions, [67-69].
  • The Phenomena of it’s Belts, [70].
  • Has no difference of seasons, [71].
  • Has four Moons, [72],
    • their grand Period, [73],
    • the Angles which their Orbits subtend as seen from the Earth, [74],
    • most of them are eclipsed in every revolution, [75].
  • The great difference between it’s equatoreal and polar Diameters, [76].
  • The inclination of it’s Orbit, and place of it’s Ascending Node, [77].
  • The Sun’s light 3000 times as strong on it as Full Moon-light is on the Earth, [85].
  • Is probably inhabited, [86].
  • The amazing strength required to put it in motion, [158].
  • The figures of the Paths described by it’s Satellites, [269].
• L.
• Light, the inconceivable smallness of it’s particles, [165],
  • • and the dreadful mischief they would do if they were larger, [166].
  • It’s surprising velocity, [166],
    • compared with the swiftness of the Earth’s annual motion, [197].
  • Decreases as the square of the distance from the luminous body increases, [169].
  • Is refracted in passing through different Mediums, [171-173].
  • Affords a proof of the Earth’s annual motion, [197], [219].
  • In what time it comes from the Sun to the Earth, [216],
    • this explained by a figure, [217].
• Limits of Eclipses, [317].
• Line, of the Nodes, what, [317];
  • • has a retrograde motion, [319].
  • Of Sines and Chords, how to make, [369].
• Long (Rev. Dr.) his method of comparing the quantity of the surface of dry land with that of the Sea, [51].
  • His glass sphere, [126].
• Longitude, how found, [207-213].
• Lucid Spots in the Heavens, [401].
• Lunar Cycle deficient, [422].
• M.
• Magellanic Clouds, [402].
• Man, of a middle size, how much pressed by the weight of the Atmosphere, [175];
  • why this pressure is not felt, ib.
• Mars, it’s Diameter, Period, Distance, and other Phenomena, [64-67].
• Matter, it’s properties, [99].
• Mean Anomaly, what, [239].
• Mercury, it’s Diameter, Period, Distance, &c. [22].
  • Appears in all the shapes of the Moon, [23].
  • When it will be seen on the Sun, [24].
  • The inclination of it’s Orbit and Place of it’s Ascending Node, ib.
  • It’s Path delineated, [138].
  • Experiment to shew it’s Phases and apparent Motion, [142].
• Mercury (Quicksilver) in the Barometer, why not affected by the Moon’s raising Tides in the Air, [311].
• Meridian, first, [207].
  • Line, how to draw one, [226].
• Milky Way, what, [400].
• Months, Jewish, Arabian, Egyptian, and Grecian, [415].
• Moon, her Diameter and Period, [52].
  • Her phases, [53], [255].
  • Shines not by her own light, [54].
  • Has no difference of seasons, [55].
  • The Earth is a Moon to her, [56].
  • Has no Atmosphere of any visible Density, [58];
    • nor Seas, [59].
  • How her inhabitants may be supposed to measure their year, [62].
  • Her light compared with day-light, [85].
  • The excentricity of her Orbit, [98].
  • Is nearer the Earth now than she was formerly, [163].
  • Appears bigger in the Horizon than at any considerable height above it, and why, [187];
    • yet is seen much under the same Angle in both cases, [188].
  • Her surface mountainous, [252]:
    • if smooth she could give us no light, ib.
  • Why no hills appear round her edge, [253].
  • Has no Twilight, [254].
  • Appears not always quite round when full, [256].
  • Her phases agreeably represented by a globular Stone viewed in Sun-shine when she is above the Horizon, and the observer placed as if he saw her on the top of the Stone, [258].
  • Turns round her Axis, [262].
  • The length of her Solar and Sidereal Day, ib.
  • Her periodical and synodical revolution represented by the motions of the hour and minute hands of a Watch, [264].
  • Her Path delineated, and shewn to be always concave to the Sun, [265-268].
  • Her motion alternately retarded and accelerated, [267].
  • Her gravity toward the Sun greater than toward the Earth at her Conjunction, and why she does not then abandon the Earth on that account, [268].
  • Rises nearer the time of Sun-set when about the full in harvest for a whole week than when she is about the full at any other time of the year, and why, [273-284]:
    • this rising goes through a course of increasing and
    • decreasing benefit to the farmers every 19 years, [292].
  • Continues above the Horizon of the Poles for fourteen of our natural Days together, [293].
  • Proved to be globular, [314].
    • and to be less than the Earth, [315].
  • Her Nodes, [317].
    • ascending and descending, [318].
    • their retrograde motion, [319].
  • Her acceleration proved from antient Eclipses, [322], n.
  • Her Apogee and Perigee, [336].
  • Not invisible when she is totally eclipsed, and why, [346].
  • How to calculate her Conjunctions, Oppositions, and Eclipses, [355-390].
  • How to find her age in any Lunation by the Golden Number, [423].
• Morning and Evening Star, what, [145].
• Motion, naturally rectilineal, [100].
  • Apparent, of the Planets as seen by a spectator at rest on the outside of all their Orbits, [133];
    • and of the Heavens as seen from any Planet, [154].
• N.
• Natural Day, not compleated in the time that the Earth turns round it’s Axis, [222].
• New and Full Moon, to calculate the times of [355].
• New Stars, [403],
  • cannot be Comets, [404].
• New Style, it’s original, [414].
• Nicias’s Eclipse, [328].
• Nodes, of the Planet’s Orbits, their places in the Ecliptic, [20].
  • Of the Moon’s Orbit, [317].
    • their retrograde motion, [319].
• Nonagesimal Degree, what, [259].
• Number of Direction, [426].
• O.
• Objects, we often mistake their bulk by mistaking their distance, [185].
  • Appear bigger when seen through a fog than through clear Air, and why, ib.
    • this applied to the solution of the Horizontal Moon, [187].
• Oblique Sphere, what, [131].
• Olympiads, what, [323]. n.
• Orbits of the Planets not solid, [21].
• Orrery described, [434], [435], [436].
• P.
• Parallax, Horizontal, what, [190].
• Parallel Sphere, what, [131].
• Path of the Moon, [265], [266], [267].
  • Of Jupiter’s Moons, [269].
• Pendulums, their vibrating slower at the Equator than near the Poles proves that the Earth turns on it’s Axis, [117].
• Penumbra, what, [336].
  • It’s velocity on the Earth in Solar Eclipses, [337].
• Period of Eclipses, [320], [326].
• Phases of the Moon, [252-268].
• Planets, much of the same nature with the Earth, [11].
  • Some have Moons belonging to them, [12].
  • Move all the same way as seen from the Sun, but not as seen from one another, [18].
  • Their Moons denote them to be inhabited, [86].
  • The proportional breadth of the Sun’s Disc as seen from each of them, [87].
  • Their proportional bulks as seen from the Sun, [88].
  • An idea of their distances from the Sun, [89].
  • Appear bigger and less by turns, and why, [90].
  • Are kept in their Orbits by the power of gravity, [101], [150-158].
  • Their motions very irregular as seen from the Earth, [137].
  • The apparent motions of Mercury and Venus delineated by Pencils in an Orrery, [138].
  • Elongations of all the rest as seen from Saturn, [147].
  • Describe equal areas in equal times, [153].
  • The excentricities of their Orbits, [155].
  • In what times they would fall to the Sun by the power of gravity, [157].
  • Disturb one another’s motions, the consequence thereof, [163].
  • Appear dimmer when seen through telescopes than by the bare eye, the reason of this, [170].
• Planetary Globe described, [439].
• Polar Circles, [198].
• Poles, of the Planets, what, [19].
  • Of the world, what, [122].
  • Celestial, seem to keep on the same points of the Heavens all the year, and why, [196].
• Projectile Force, [150];
  • if doubled would require a quadruple power of gravity to retain the Planets in their Orbits, [153].
  • Is evidently an impulse from the hand of the Almighty, [161].
• Precession of the Equinoxes, [246-251].
• Ptolemean System absurd, [96], [140].
• R.
• Rays of Light, if not disturbed, move in straight lines, and hinder not one another’s motions, [168].
  • Are refracted in passing through different mediums, [171].
• Reflection of the Atmosphere causes the Twilight, [177].
• Refraction of the Atmosphere bends the rays of light from straight lines, and keeps the Sun and Moon longer in sight than they would otherwise be, [178].
  • A surprising instance of this, [183].
  • Must be allowed for in taking the Altitudes of the celestial bodies, ib.
• Right Sphere, [131].
• S.
• Satellites; the times of their revolutions round their primary Planets, [52], [73], [80].
  • Their Orbits compared with each other, with the Orbits of the primary Planets, and with the Sun’s circumference, [271].
  • What sort of Curves they describe, [272].
• Saturn, with his Ring and Moon’s, their Phenomena, [78], [79], [82].
  • The Sun’s light 1000 times as strong to him as the light of the Full Moon is to us, [85].
  • The Phenomena of his Ring farther explained, [204].
• Our blessed Saviour, the darkness at his crucifixion supernatural, [352].
  • The prophetic year of his crucifixion found to agree with an astronomical calculation, [432].
• Seasons, different, illustrated by an easy experiment, [200];
  • • by a figure, [202].
• Shadow, what, [312].
• Sidereal Time, what, [221];
  • • the number of Sidereal Days in a year exceeds the number of Solar Days by one, and why, [222].
  • An easy method for regulating Clocks and Watches by it, [223].
• Signs of the Zodiac, their names and characters, [91], [365].
  • How they are numbered by Astronomers, [354].
• Sines, line of, how to make, [369].
• Smith, (Rev. Dr.) his companion between Moon-light and Day-light, [85].
  • His demonstration that light decreases as the square of the distance from the luminous body increases, [169].
  • (Mr. George) his Dissertation on the Progress of a Solar Eclipse, [321-324].
• Solar Astronomer, the judgment he might be supposed to make concerning the Planets and Stars, [135], [136].
• Sphere, parallel, oblique, and right, [131].
  • It’s Circles, [198].
• Spring and Neap Tides, [302].
• Stars, their vast distance from the Earth, [3], [196].
  • Probably not all at the same distance, [4] Shine by their own light, and are therefore Suns [7],
    • probably to other worlds, [8] A demonstration that they do not move round the Earth, [111].
  • Have an apparent slow motion round the Poles of the Ecliptic, and why, [251].
  • A catalogue of them, [399].
  • Cloudy, [402].
  • New, [403].
  • Some of them change their places, [404].
• Starry Heavens have the same appearance from any part of the Solar System, [132].
• Sun appears bigger than the Stars, and why, [4] Turns round his Axis, [18].
  • His proportional breadth as seen from the different Planets, [87].
  • Describes unequal arcs above and below the Horizon at different times, and why, [130].
  • His Center the only place from which the true motions of the Planets could be seen, [135].
  • Is for half a year together visible at each Pole in it’s turn, and as long in visible, [200], [294].
  • Is nearer the Earth in Winter than in Summer, [205].
  • Why his motion agrees so seldom with the motion of a well regulated Clock, [224-245].
  • Would more than fill the Moon’s Orbit, [271].
  • Proved to be much bigger than the Earth, and the Earth to be bigger than the Moon, [315].
  • To calculate his true place, [360].
• Systems, the Solar, [17-95];
  • the Ptolemean, [96];
  • the Tychonic, [97].
• T.
• Table, of the Periods, Revolutions, Magnitudes, Distances, &c. of the Planets, facing § [99].
  • Of the Air’s rarity, compression, and expansion at different heights, [174].
  • Of refractions, [182].
  • For converting time into motion, and the reverse, [220].
  • For shewing how much of the celestial Equator passes over the Meridian in any part of a mean Solar Day; and how much the Stars accelerate upon the mean Solar time for a month, [221].
  • Of the first part of the Equation of time, [229];
    • of the second part, [241].
  • Of the precession of the Equinox, [247].
  • Of the length of Sidereal, Julian, and Tropical Years, [251].
  • Of the Sun’s place and Anomaly, following [251].
  • Of the Equation of natural Days, following [251]
  • Of the Conjunctions of the hour and minute hands of a Watch, [264].
  • Of the Curves described by the Satellites, [272].
  • Of the difference of time in the Moon’s rising and setting on the parallel of
    • London every day during her course round the Ecliptic, [277].
  • Of Eclipses, [327].
  • For calculating New and Full Moons and Eclipses, following [390].
  • Of the Constellations and number of the Stars, [399].
  • Of the Jewish, Egyptian, Arabic, and Grecian months, [415].
  • For inserting the Golden Numbers right in the Calendar, [423].
  • Of the times of all the New Moons for 76 years, [424].
  • Of remarkable Æras or Events, [433].
  • Of the Golden Number, Number of Direction, Dominical Letter and Days of the Months, following [433].
• Thales’s Eclipse, [323].
• Thucydides’s Eclipse [324].
• Tides, their Cause and Phenomena, [295-311].
• Tide-Dial described, [441].
• Trajectorium Lunare described, [440].
• Tropics, [198].
• Twilight, none in the Moon, [254].
• Tychonic System absurd, [97].
• U.
• Universe, the Work of Almighty Power, [5], [161].
• Up and down, only relative terms, [122].
• Upper or under side of the Earth no such thing, [123].
• V.
• Velocity of Light compared with the velocity of the Earth in it’s annual Orbit, [197].
• Venus, her bulk, distance, period, length of days and nights, [26].
  • Shines not by her own light, ib.
  • Is our morning and evening Star, [28].
  • Her Axis, how situated, [29].
  • Her surprising Phenomena, [29-43].
  • The inclination of her Orbit, [45].
  • When she will be seen on the Sun, ib.
  • How it may probably be soon known if she has a Satellite, [46].
  • Appears in all the Shapes of the Moon, [23], [141].
  • An experiment to shew her phases and apparent motion, [141].
• Vision, how caused, [167].
• W.
• Weather, not hottest when the Sun is nearest to us, and why, [205].
• Weight, the cause of it, [122].
• World not eternal, [164].
• Y.
• Year, [407],
  • Great, [251],
  • Tropical, [408],
  • Sidereal, [400],
  • Lunar, [410],
  • Civil, [411],
  • Bissextile, ib.
  • Roman, [413],
  • Jewish, Egyptian, Arabic, and Grecian, [415],
  • how long it would be if the Sun moved round the Earth, [111].
• Z.
• Zodiac, what, [397].
  • How divided by the antients, [398].
• Zones, what, [199].

DIRECTIONS to the BOOKBINDER.

The Orrery Plate is to front the Title Page.

Plate I	fronting Page 5
II	39
III	49
IV	73
V	81
VI	97
VII	125
VIII	147
IX	147
X	157
XI	179
XII	203
XIII	279

Footnotes

[1]. Dr. Young’s Night Thoughts.

[2]. If a thread be tied loosely round two pins stuck in a table, and moderately stretched by the point of a black lead pencil carried round by an even motion and light pressure of the hand, an oval or ellipsis will be described; the two points where the pins are fixed being called the foci or focuses thereof. The Orbits of all the Planets are elliptical, and the Sun is placed in or near to one of the foci of each of them: and that in which he is placed, is called the lower focus.

[3]. Astronomers are not far from the truth, when they reckon the Sun’s center the lower focus of all the Planetary Orbits. Though strictly speaking, if we consider the focus of Mercury’s Orbit to be in the Sun’s center, the focus of Venus’s Orbit will be in the common center of gravity of the Sun and Mercury; the focus of the Earth’s Orbit in the common center of gravity of the Sun, Mercury, and Venus; the focus of the Orbit of Mars in the common center of gravity of the Sun, Mercury, Venus, and the Earth; and so of the rest. Yet, the focuses of the Orbits of all the Planets, except Saturn, will not be sensibly removed from the center of the Sun; nor will the focus of Saturn’s Orbit recede sensibly from the common center of gravity of the Sun and Jupiter.

[4]. As represented in [Plate III.] Fig. I. and described in § [138].