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CONTENTS.

.

89

PAGE.

Esplanation of the principal Terms relating to As.

tronomy, Chronology, and the astronomical

Parts of Geography, with occasional Illustra.

trations and Remarks,

5

Table of the Motions and Distances of the

Planets,

28

Table of the Satellites,

29

CHAP. I. Of Astronomy in general,

33

II. A brief Description of the SOLAR SYSTEM, 40

III. The COPERNICAN SYSTEM demonstrated to be

true,

77

IV. The Phenomena of the Heavens as seen from dif-

ferent Parts of the Earth,

V. The Phenomena of the Heavens as seen from differ-

ent Parts of the Solar Sytem,

97

VI. - The Ptolemean System refuted. The Motions and

Phases of Mercury and Venus explained, 102

VII. The physical Causes of the Motions of the Planets.

The Excentricities of their Orbits. The Times

in which the Action of Gravity would bring

them to the Sun. ARCHIMEDES' ideal Problem

for moving the Earth. The World not eternal, 109

VIII. Of Light. Its proportional Quantities on the dif-

ferent Planets. Its Refractions in Water and

Air. The Atmosphere ; its Weight and Proper-

ties. The horizontal Moon,

118

IX. The Method of finding the Distances of the Sun,

Moon, and Planets,

134

X. The Circles of the Globe described. The different

Lengths of Days and Nights, and the Vicissi-

tudes of Seasons, explained. The Explanation of

the Phenomena of Saturn's Ring, concluded, 142

XI. The Method of finding the Longitude by the

Eclipses of Jupiter's Satellites The amazing

Velocity of Light demonstrated by these Eclip-

ses,

154

XII. Of Solar and Sidereal Time,

162

XIII. Of the Equation of Time,

167

XIV. Of the Precession of the Equinoxes,

183

XV. The Moon's Surface mountainous: Her Phases

described: Her Path, and the Paths of Jupi.

ter's Moons delineated : The Proportions of the

Diameters of their Orbits, and those of Saturn's

Moons to each other, and to the Diameter of

the Sun,

219

XVI. The Phenomena of the Harvest Moon explained by

a common Globe: The Years in which the

Harvest Moons are least and most beneficial,

from 1751 to 1861. The long Duration of Moon-

light at the Poles in Winter,

235

XVII. Of the Ebbing and Flowing of the Sea,

251

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CHAP. XVIII. Of Eclipses: Their Number and Periods. A large

Catalogue of Ancient and Modern Eclipses, 263

XIX. Shewing the Principles on which the following

Astronomical Tables are constructed, and the

Method of calculating the Times of New and

Full Moons and Eclipses, by them,

320

XX. Of the fixed Stars,

370

XXI. Of the Division of Time. A perpetual Table of

New Moons. The Times of the Birth and Death

of CHRIST. A Table of remarkable Æras or

Events,

391

XXII. A Description of the astronomical Machinery,

serving to explain and illustrate the foregoing

Part of this Treatise,

432

XXIII. The Method of finding the Distances of the Planets

from the Sun,

465
Art. I. Concerning Parallaxes, and their Use in general, 467

Art. II. Shewing how to find the horizontal Parallax of

Venus by Observation, and from thence, by

Analogy, the Parallax and Distance of the Sun,

and of all the Planets from him,

472

Art. III. Containing Doctor HALLEY's Dissertation on

the Method of finding the Sun's Parallax and

Distance from the Earth, by the Transit of

Venus over the Sun's Disc, June the 6th, 1761.

Translated from the Latin in Motte's Abridg-

ment of the Philosophical Transactions, Vol. I.

page 243; with additional Notes,

482

Arr. IV. Shewing that the whole Method proposed by the

Doctor cannot be put in Practice, and why, 498

Art. V. Shewing how to project the Transit of Venus on

the Sun's Disc, as seen from different Places of

the Earth ; so as to find what its visible Dura-

tion must be at any given Place, according to

any assumed Parallax of the Sun ; and from the

observed Intervals between the Times of Ve.

nus's Egress from the Sun at particular Places,

to find the Sun's true horizontal Parallax, 500

ART. VI. Concerning the Map of the Transit,

520

Art. VII. Containing an Account of Mr. Horrox's Observa.

tion of the Transit of Venus over the Sun, in

the Year 1639; as it is published in the Annual

Register for the Year 1761,

521

Art. VIII. Containing a short Account of some Observations

of the Transit of Venus, A D. 1761, June 6th ;

and the Distance of the Planets from the Sun,

as deduced from those Observations.

528

ASTRONOMY EXPLAINED.

CHAP. L

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use of astrono

Of Astronomy in general. 1.

F all the sciences cultivated by mankind, The gener

astronomy is acknowledged to be, and as undoubtedly is, the most sublime, the most inter-my. esting, and the most useful. For, by knowledge derived from this science, not only the magnitude of the earth is discovered, the situation and extent of the countries and kingdoms upon it ascertained, trade and commerce carried on to the remotest parts of the world, and the various products of several countries distributed for the health, comfort, and conveniency of its inhabitants; but our very faculties are enlarged with the grandeur of the ideas it conveys, our minds exalted above the low contracted prejudices of the vulgar, and our understandings clearly convinced, and affected with the conviction, of the existence, wisdom, power, goodness, immutability, and superintendency of the SUPREME BEING. So that, without an hyperbole,

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" An undevout astronomer is mad.*"

2. From this branch of knowledge we also learn by what means or laws the Almighty carries on, and continues, the wonderful harmony, order, and connexion, observable throughout the planetary system; and are led, by very powerful arguments, to form this pleasing deduction—that minds capable

* Dr. Young's Night Thoughts,

E

Sun.

of such deep researches, not only derive their origin from that adorable Being, but are also incited to aspire after a more perfect knowledge of his na

ture, and a stricter conformity to his will. The Earth 3. By astronomy, we discover that the Earth is but a point at so great a distance from the Sun, that it seen from from the thence it would appear no larger than a point; al

though its circumference is known to be 25,020 miles. Yet even this distance is so small, compared with that of the fixed stars, that if the orbit in which the Earth moves round the Sun were solid, and seen from the nearest star, it would likewise appear no. larger than a point ; although it is about 162 mil. hons of miles in diameter. For the Earth, in go. ing round the Sun, is 162 millions of miles nearer to some of the stars at one time of the year, than at another; and yet their apparent magnitudes, situations and distances from one another, still remain the same; and a telescope which magnifies above 200 times, does not sensibly magnify them. This proves them to be at least 400 thousand times farther from us than we are from the Sun.

4. It is not to be imagined that all the stars are placed in one concave surface, so as to be equally distant from us; but that they are placed at im. mense distances from one another, through unli. mited space. So that there may be as great a distance between any two neighbouring stars, as between the Sun and those which are nearest to him.

An observer, therefore, who is nearest any fixed The stars star, will look upon it alone as a real Sun; and conare suns, sider the rest as so many shining points, placed at

equal distances from him in the firmament.

5. By the help of telescopes we discover thousands of stars which are invisible to the bare eye; and

the better our glasses are, still the more stars become and innu- visible: so that we can set no limits either to their merable. number or their distances. The celebrated Huy.

GENS carried his thoughts so far, as to believe it not impossible that there may be stars at such inconceivable distances, that their light has not yet reached the Earth since its creation ; although the velocity of light be a million of times greater than the velocity of a cannon-ball, as shall be demonstrated afterward, 197. 216.--And, as Mr. ADDISON very justly observes, this thought is far from being extravagant, when we consider that the universe is the work of infinite power, prompted by infinite goodness; having an infinite space to exert it. self in; so that our imaginations can set no bounds to it.

6t The Sun appears very bright and large in Why the comparison with the fixed stars, because we keep pears Tarconstantly near the Sun, in comparison with our ger than immense distance from the stars. For, a spectator

the stars. placed as near to any star as we are to the Sun, would see that star a body as large and bright as the Sun appears to us : and a spectator as far distant from the sun as we are from the stars, would see the Sun as small as we see a star, divested of all its circumvolving planets; and would reckon it one of the stars in numbering them.

7. The stars, being at such immense distances The stars from the Sun, cannot possibly receive from him so are not en.

lightened strong a light as they seem to have; nor any bright- by the ness sufficient to make them visible to us. For the Sun. Sun's rays must be so scattered and dissipated before they reach such remote objects, that they can never be transmitted back to our eyes, so as to render these objects visible by reflection. The stars therefore shine with their own native and unborrowed lustre, as the Sun does. And since each par. ticular star, as well as the Sun, is confined to a particular portion of space, it is plain that the stars are of the same nature with the Sun.

8. It is no ways probable that the Almighty, who always acts with infinite wisdom, and does nothing in vain, should create so many glorious suns, fit for so many important purposes, and place them at such distances from one another, without pro

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