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the longitude of the perihelion; and

Tis the time of perihelion passage;

that of the ascending node for the epoch of the perihelion;

4, the inclination to the ecliptic; a, the semi-axis; e, the excentricity; P, the period in days.

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N. B. The reader will find a complete list of elements of all known comets up to June, 1847, by all their several computors, in Prof. Encke's edition of Olbers's Abhandlung über die leichteste und bequemste Methode die Bahn eines Cometen zu berechnen." The list is compiled by Dr. Galle. It contains orbits of 178 distinct comets. From an examination of these orbits we collect the following, as a more correct statement of cometary statistics than that in art. 601. viz.:- Retrograde comets under 10° inclination, 3 out of 15; under 20o, 9 out of 29. Retrograde comets, moving in orbits sensibly elliptic, under 170 inclination, 0 out of 9. In such orbits, of all inclinations from 0 to 90°, 11 out of 37. Thus we see that the induction of that article is materially strengthened by the enlarged field of comparison.

INDEX.

N.B. The references are to the articles, not to the pages.

attached to a reference number indicates that the reference extends to the article cited, and
several subsequent in succession.

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Aboul Wefa, 705.

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Acceleration, secular, of moon's mean Argo, nebulæ in, 887. Irregular star ʼn

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in constellation, 830.

Ascension, right, 108. (See Right ascen-
sion.)

Asteroids, their existence suspected pre-
vious to their discovery, 505. Ap-
pearance in telescopes, 525. Gravity
on surface of, 525. Elements, Appen-
dix, Synoptic Table.
Astræa, discovery of, 505.
Astrometer, 783, 784.
Astronomy. Etymology, 11. General
notions, 11.

Atmosphere, constitution of, 33... Pos-
sible limit of, 36. Its waves, 37.
Strata, 37. Causes refraction, 38.
Twilight, 44. Total mass of, 148.
Of Jupiter, 513.

Attraction of a sphere, 445-450. (See
Gravitation.)

Augmentation of moon's apparent dia-
meter, 404.

Augustus, his reformation of mistakes
in the Julian calendar, (919.) Era
of, 926.

Australia, excessive summer tempera-
ture of, 369.

Axis of the earth, 82. Rotation per-
manent, 56. Major of the earth's
orbit, 373. Of sun's rotation, 392.
Axis of a planetary orbit. Momentary
variation of, caused by the tangential
force only, 658. 660. Its variations
periodical, 661... Invariability of,
and how understood, 668.
Azimuth, 103.-and altitude instru-
ment, 187.

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Of

of, 291... Bremiker's, 506, and note.
Chinese records of comets, 574.
irregular stars, 831.
Chronometers, how used for determining
differences of longitude, 255.
Circle, arctic and antarctic, 94. Verti-

cal, 100. Hour, 106. Divided, 163.
Meridian, 174. Reflecting, 197. Re-
peating, 198. Galactic, 793.
Clepsydra, 150.

Clock, 151. Error and rate of, how
found, 253.

Clouds, greatest height of, 34. Magel-
lanic, 892...

Clusters of stars, 864... Globular, 867.
Irregular, 869.

Collimation, line of, 155.

Collimator, 178...

Coloured stars, 851...

Colures, 307.

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treme tenuity of, 558. General de-
scription of, 560. Motions of, and
described, 561... Parabolic, 564.
Elliptic. 567... Hyperbolic, 564. Di-
mensions of, 565. Of Halley, 567...
Of Cæsar, 573. Of Encke, 576. Of
Biela, 579. Of Faye, 584. Of
Lexell, 585. Of De Vico, 586. Of
Brorsen, 587.

Of Peters, 588. Sy-
nopsis of elements (Appendix). In-
crease of visible dimensions in re-
ceding from the sun, 571.580. Great,
of 1843, 589... Its supposed identity
with many others, 594... Interest at-
tached to subject, 597. Cometary
statistics, and conclusions therefrom,
601.

Commensurability (near) of mean mo-
tions; of Saturn's satellites, 550. Of
Uranus and Neptune, 669. and note.
Of Jupiter and Saturn, 720. Earth
and Venus, 726. Effects of, 719.
Compensation of disturbances, how ef-
fected, 719. 725.

Compression of terrestrial spheroid, 221.
Configurations, inequalities depending
on, 655...

Conjunctions, superior and inferior, 473.
Perturbations chiefly produced at, 713.
Consciousness of effect when force is
exerted, 439.
Constellations, 60. 301.

How brought
into view by change of latitude, 52.
Rising and setting of, 58.
Copernican explanation of diurnal mo-
tion, 76. Of apparent motions of
sun and planets, 77.

Correction of astronomical observations,
324... s. Uranographical summary,
view of, 342...

Culminations, 125. Upper and lower,
126.

Cycle, of conjunctions of disturbing
and disturbed planets, 719. Meto-
nic, 926. Callippic, ib. Solar, 921
Lunar, 922. Of indictions, 923.

D.

Day, solar, lunar, and sidereal, 143.
Ratio of sidereal to solar, 305. 909.
911. Solar unequal, 146. Mean
ditto, invariable, 908. Civil and
astronomical, 147. Intercalary, 916.
Days elapsed between principal chro-
nological eras, 926. Rules for reckon-
ing between given dates, 927.
Declination, 105. How obtained, 295.
Definitions, 82...

912.

Degree of meridian, how measured, 210. | Egyptians, ancient, their chronology,
Error admissible in, 215. Length
of in various latitudes, 216. 221.
Diameters of the earth, 220, 221.
planets, synopsis, Appendix. (See
also each planet.)

Of

Dilatation of comets in receding from
the sun, 578.
Dione, 548.

Discs of stars, 816.

Distance of the moon, 403.; the sun,
357.; fixed stars, 807. 812...; polar,

105.

Districts, natural, in heavens, 302.
Disturbing forces, nature of, 609... Ge-
neral estimation of, 611. Numerical
values, 612. Unresolved in direc-
tion, 614. Resolution of, in two
modes, 615. 618. Effects of each
resolved portion, 616... On moon,
expressions of, 676. Geometrical re-
presentations of, 676. 717.
Diurnal motion explained, 58. Paral-
lax, 339. Rotation, 144.
Double refraction, 202. Image micro-
meter, a new, described, 203. Co-
met, 580. Nebula, 878.
Double Stars, 833... Specimens of each
class, 835. Orbitual motion of, 839.
Subject to Newtonian attraction, 843.
Orbits of particular, 843. Dimen-
sions of these orbits, 844. 848. Co-
loured, 851... Apparent periods af-
fected by motion of light, 863.
Dove, his law of temperature, 370.

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Elements of a planet's orbit, 493. Va-
riations of, 652... Of double star or-
bits, 843. Synoptic table of planet-
ary, &c., Appendix.

Ellipse, variable, of a planet, 653. Mo-
mentary or osculating, 654.
Elliptic motion a consequence of gravi-
tation, 446. Laws of, 489... Their
theoretical explanation, 491.
Ellipticity of the Earth, 221.
Elongation, 341. Greatest, of Mercury
and Venus, 467.
Enceladus, 548., note.
Encke, comet of, 576. His hypothesis
of the resistance of the ether, 577.
Epoch, one of the elements of a planet's
orbit, 496. Its variation not inde-
pendent, 730. Variations incident

on, 731. 744.
Equation of light, 335. Of the center,
375. Of time, 379. Lunar, 452.
Annual, of the moon, 738.
Equator, 84.
Equatorial, 185.

Equilibrium, figure of, in a rotating
body, 224.

Equinoctial, 97. Time, 935.
Equinox, 293. 303.

Equinoxes, precession of, 312. Its ef-
fects, 313. In what consisting, 314...
Its physical cause explained, 642...
Eras, chronological list of, 926.
Errors, classification of, 133. Instru-
mental, 135... Their detection, 140.
Destruction of accidental ones by
taking means, 137. Of clock, how
obtained, 293.

Establishment of a port, 754.
Ether, resistance of, 577.
Evection of moon, 748.
Excentricities, stability of Lagrange's
theorem respecting, 701.
Excentricity of earth's orbit, 354. How
ascertained, 377. Of the moon's, 405.
Momentary perturbation of, investi-
gated, 670. Application to lunar
theory, 688. Variations of, in orbits
nearly circular, 696. In excentric
orbits, 697. Permanent inequalities
depending on, 719.

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of place, 670, 671. Path of, in virtue |
of both elements of disturbing force,
704. Traced in the case of the
moon's variation, 706... And paral-
lactic inequality, 712. Circulation of,
about a mean situation in planetary
perturbations, 727.

Force, metaphysical conception of, 439.
Forced vibration, principle of, 650.
Forces, disturbing. See Disturbing force.

G.

Galactic circle, 793. Polar distance,
ib.

Galaxy composed of stars, 302.

Sir

W. Herschel's conception of its form
and structure, 786. Distribution of
stars generally referable to it, 786.
Its course among the constellations,
787... Difficulty of conceiving its
real form, 792. Telescopic analysis
of, 797. In some directions unfathom-
able, in others not, 798.
Gulle, Dr., 506. Finds Neptune in
place indicated by theory, 768.
Galloway, his researches on the sun's
proper motion, 855.

Gasparis, Sig. De, discovers a new
planet (Appendix).
Gauging the heavens, 793.

Gay Lussac, his aëronautic ascent, 32.
Geocentric longitude, 503. Place, 371.

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Hansen. His detection of long ine-
qualities in the moon's motions, 745...
Harding discovers Juno, 505.
Heat, supply of, from sun alike in
summer and winter, 368. How kept
up, 400. Sun's expenditure of esti-
mated, 397. Received from the sun
by different planets, 508. Endured
by comets in perihelio, 592.
Hebe, discovery of, 505.

Heights above the sea, how measured,
286. Mean, of the continents, 289.
Heliocentric place, 500.
Heliometer, 201.

Hemispheres, terrestrial and aqueous,284.
Herschel, Sir Wm., discovers Uranus,
505, and two satellites of Saturn, 548.
His method of gauging the heavens,
793. Views of the structure of the
Milky Way, 786. Of nebular sub-
sidence, and sidereal aggregation, 869.
874. His catalogues of double stars,
835. Discovery of their binary con-
nexion, 839. Of the sun's proper
motion, 854. Classifications of ne-
bulæ, 868. 879. note.

Horizon, 22. Dip of, 23. 195. Rational
and sensible, 74. Celestial, 98. Arti-
ficial, 163.

Horizontal point of a mural circle, how
determined, 175...

Hour circles, 106.; angle, 107.; glass,

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Iapetus, 548.
Inclination of the moon's orbit, 406. Of
planet's orbits disturbed by orthogo-
nal force, 619. Physical importance
of, as an element, 632. Momentary
variation of, estimated, 633. Crite-
rion of momentary increase or dimi-
nution, 635. Its changes periodical
and self-correcting, 636. Application
to case of the moon, 638.
Inclinations, stability of, Lagrage's theo-
rem, 639. Analogous in their per-
turbations to excentricities, 699.
Indictions, 923.
Inequality. Parallactic of moon, 712.
Great, of Jupiter and Saturn, 720...
Inequalities, independent of excentri-
city, theory of, 702... Dependent
on, 719.
Intercalation, 916.

Iris, discovery of, 505.
Iron, meteoric, 888.

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