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 20°, 9 out of 29. Retrograde comets, moving in orbits sensibly elliptic, under 17° 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.

motion, 740.

Adams, 506. 767.

Adjustment, errors of, in instruments,
136. Of particular instruments. (See
those instruments.)

Etna, portion of earth visible from, 32.
Height of, 32. note.

Air, rarefaction of, 33. Law of density,
37.
Refractive power affected by
moisture, 41.
Airy, G. B. Esq., his results respecting
figure of the earth, 220. Researches
on perturbations of the earth by Ve-
nus, 726. Rectification of the mass
of Jupiter, 757.
Algol, 821.

Altitude and azimuth instrument, 187.
-s. Equal, method of, 188.
Andromeda, nebula in, 874.
Angle of position, 204. Of situation, 311.
Angles, measurement of, 163. 167. Hour,
107.

Angular velocity, law of, variation of,
350.

Anomalistic year, 384.

Anomaly of a planet, 499.
Annular nebulæ, 875.

Apex of aberration, 343. Of parallax,
343. Of refraction, 343. Solar, 854.
Of shooting stars, 902. 904.

Aphelion, 368.

Apogee of moon, 406. Period of its re-
volution, 687.
Apsides, 406.

Motion of investigated,
675. Application to lunar, 676...
Motion of, illustrated by experiment,

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... Possi-
ble limit of, 36. Its waves, 37. Strata,
37. Causes refraction, 38. Twi-
light, 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 perma
nent, 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 instrument,
187.

B.

Barometer, nature of its indication, 33.
Use in calculating refraction, 43. In
determining heights, 287.

Belts of Jupiter, 512. Of Saturn, 514.
Benzenberg's principle of collimation,
179.

Bessel, his results respecting the figure
of the earth, 220. Discovers parallax
of 61 Cygni, 812.

Biela's comet, 579...

Biot, his aëronautic ascent, 32.
Bode, his (so called) law of planetary
distances, 505. Violated in the case
of Neptune, 507.

Borda, his principle of repetition, 198.
Bouvard, his suspicion of extraneous
influence on Uranus, 760.

C.

Cæsar, his reform of the Roman calen-
dar, 917.

Calendar, Julian, 917. Gregorian, 914...
Cause and effect, 439, and note.
Centre of the earth, 80. Of the sun, 462.
Of gravity, 360. Revolution about,
452.
Centrifugal force. Elliptic form of earth
produced by, 224. Illustrated, 225.
Compared with gravity, 229.
Of a
body revolving on the earth's surface,
452.

Ceres, discovery of, 505.
Challis, Prof., 506, note.
Charts, celestial, 111. Construction of,

291... Bremiker's, 506, and note.
Chinese records of comets, 574. Of ir-
regular 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.

590. Tails of, 556...566. 599. Ex-
treme tenuity of, 558. General de-
scription of, 560. Motions of, and
described, 561... Parabolic, 564. El-
liptic, 567... Hyperbolic, 564. Di-
mensions of, 565. Of Halley, 567...

Of

Of Lex-

Of Cæsar, 573. Of Encke, 576.
Biela, 579. Of Faye, 584.
ell, 585.
Of De Vico, 586.
sen, 587. Of Peters, 588.

Of Bror-

Synopsis

of elements (Appendix). Increase of
visible dimensions in receding from
the sun, 571. 580. Great, of 1843,
589... Its supposed identity with
many others, 594... Interest attached
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 ex-
erted, 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. Metonic, 926.
Callippic, ib. Solar, 921. Lunar 922.
Of indictions, 923.

D.

Flora, discovery of, 505.
Focus, upper. Its momentary change of
place, 670, 671. Path of, in virtue of
both elements of disturbing force, 704.
Traced in the case of the moon's vari-
ation, 706... And parallactic inequa-
lity, 712. Circulation of, about a
mean situation in planetary perturba-
tions, 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 unfathomable, in
others not, 798.

Galle, 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 pla-
net (Appendix).
Gauging the heavens, 793.

Gay Lussac, his aëronautic ascent, 32.
Geocentric longitude, 503. Place, 371,
497.

Geodesical measurements,-their nature,
247...
Geography, 111, 205...

Globular clusters, 865. Their dynami-
cal stability, 866. Specimen list of,
867.

Golden number, 922.

Goodricke, his discovery of variable stars,
821...

Gravitation, how deduced from phæno-
mena, 444... Elliptic motion a con-
sequence of, 490...

Gravity, centre of, see Centre of gra-
vity.

Gravity diminished by centrifugal force,
231. Measures of, statical, 234. Dy-
namical, 235. Force of, on the moon,
433... On bodies at surface of the
sun, 440. Of other planets, see their

names.

Gregorian reform of calendar, 915...

H.

Halley. His comet, 567. First notices
proper motions of the stars, 852.
Hansen. His detection of long inequa-
lities in the moon's motions, 745...
Harding discovers Juno, 505.
Heat, supply of, from sun alike in sum-
mer and winter, 368. How kept up.
400. Sun's expenditure of, estimated
397. Received from the sun by dif
ferent planets, 508. Endured by cr
mets 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 subsi-
dence, and sidereal aggregation, 869,
874. His catalogues of double stars,
835. Discovery of their binary con-
nexion, 839. Of the sun's proper mo-
tion, 854. Classifications of nebulæ,
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,
150.

Hyperion, Appendix, Saturn's satellites.

Tapetus, 548.

I.

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, Lagrange's the-
orem, 639. Analogous in their per-
turbations to excentricities, 699.
Indictions, 923.

Inequality. Parallactic of moon, 712.
Great, of Jupiter and Saturn, 720...