CHAP. I.

Of Astronomy in general,

33

II. A brief Description of the SOLAR SYSTEM,

III. The COPERNICAN SYSTEM demonstrated to be

40

true,

77

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

ferent Parts of the Earth,

89

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

ent Parts of the Solar Sytem,

97

102

VI. The Ptolemean System refuted. The Motions and

Phases of Mercury and Venus explained,

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,

IX.

X.

The Method of finding the Distances of the Sun,

Moon, and Planets,

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,

XI. The Method of finding the Longitude by the

Eclipses of Jupiter's Satellites The amazing

Velocity of Light demonstrated by these Eclip-

ses,

XII. Of Solar and Sidereal Time,

XIII. Of the Equation of Time,

XIV. Of the Precession of the Equinoxes,

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,

118

134

142

154

162

167

183

219
PAGE

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

Catalogue of Ancient and Modern Eclipses,

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,

Of the fixed Stars,

XX.

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,

263

320

370

391

XXII. A Description of the astronomical Machinery,

serving to explain and illustrate the foregoing

Part of this Treatise,

XXIII.

The Method of finding the Distances of the Planets

from the Sun,

432

465

Concerning Parallaxes, and their Use in general, 467

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,

ART. IV.

ART. V.

ART. VI.

ART. VII.

Shewing that the whole Method proposed by the

Doctor cannot be put in Practice, and why,

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,

Concerning the Map of the Transit,

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,

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.

482

498

500

520

521

528

1.

CHAP. L

Of Astronomy in general.

ral use of

F all the sciences cultivated by mankind, The gene-
astronomy is acknowledged to be, and astrone-

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 se-
veral countries distributed for the health, comfort,
and conveniency of its inhabitants; but our very fa-
culties are enlarged with the grandeur of the ideas
it conveys, our minds exalted above the low con-
tracted prejudices of the vulgar, and our under-
standings clearly convinced, and affected with the
conviction, of the existence, wisdom, power, good-
ness, immutability, and superintendency of the
SUPREME BEING. So that, without an hy-
perbole,

"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

as seen

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 nature, 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; although 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 going 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 immense distances from one another, through unlimited 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 HuyGENS 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 itself in; so that our imaginations can set no bounds to it.

Sun ap

6t The Sun appears very bright and large in Why the comparison with the fixed stars, because we keep pears larconstantly 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 star's 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 particular 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