before the Royal Astronomical Society, on Nov. 13, such an overwhelming chain of evidence in favour of our distinguished countryman's exertions as seems to all impartial minds to have finally settled the question a.

The intellectual grandeur of this discovery will be best appreciated, so far as a non-mathematical reader is concerned, by placing in juxta-position the observed longitude of the new planet when telescopically discovered, and the computed longitudes of Adams and Le Verrier.

From this it will be seen that Le Verrier's computation proved to be slightly the more accurate of the two, a fact which in no respect militates against the equality of the merits of the two great mathematicians.

After considerable discussion Neptune was the name agreed upon for the new planet; Galle's suggestion of Janus being rejected as too significant.

'Such," in the words of Hind, "is a brief history of this most brilliant discovery, the grandest of which astronomy can boast, and one that is destined to a perpetual record in the annals of sciencean astonishing proof of the power of the human intellect."

The accompanying diagram shews the paths of Uranus and Neptune from 1781 to 1840, and will illustrate the direction of the perturbing action of the latter planet on the former.

From 1781 to 1822 it will be evident, from the direction of

The foregoing is a very bare outline of the case, which is a very interesting one. Grant (Hist. Phys. Ast., p. 165 et seq.) gives full particulars; and references may also be made to Month. Not. R.A.S., vol. vii. p. 121; Mem. R.A.S., vol. xvi. p. 385; Athenæum, Oct. 3, 1846; Adm.

Smyth's Speculum Hartwellianum, p. 405; and Sir J. Herschel's Outlines of Ast., P. 533 et seq. The French case will be found stated in Arago's Pop. Ast., vol. ii. p. 632 et seq., where the English translator's notes are very necessary.

the arrows, that Neptune tended to draw Uranus in advance of its place as computed independently of exterior perturbation.

In 1822 the two planets were in conjunction, and the only effect of Neptune was to draw Uranus farther from the Sun, without altering its longitude.

From 1822 to 1830 the effect of Neptune was to destroy the excess of longitude accumulated from 1781, and after 1830 the error in longitude changed its sign, and for some years subsequently Uranus was retarded by Neptune.

Neptune revolves round

the Sun in 60,126 days, or 1646 years, at a mean distance of 2,746,271,232 miles, which an eccentricity of 0.0087 will increase to 2,770,217,344, or diminish to 2,722,325,120 miles. The apparent diameter of Neptune only varies between 26" and 2.8". Its true diameter is about 36,600 miles-somewhat greater than that of Uranus. No compression is perceptible.

Neptune is destitute of visible spots and belts, and the period of its axial rotation is unknown, and likely to remain so. Lassell, Challis, and Bond, have at various times suspected the existence of a ring, but nothing certain is known on the subject. It would be very desirable to have a large reflector like Lord Rosse's devoted to a series of observations of this planet and Uranus, for it is nearly certain that no other existing instrument will add to our present extremely limited knowledge of the physical appearance of these planets.

Neptune is known to be attended by one satellite, discovered by Lassell in 1846, and both that observer and the late W. C. Bond subsequently obtained traces of the existence of a second, though this awaits confirmation.

The following table conveys all the information we at present possess about Lassell's confirmed satellite ::

The elements are calculated for direct motion; accordingly it will be noticed that the actual Neptunicentric motion of the satellite is retrograde-a circumstance, excepting in the case of the Uranian satellites, unparalleled in the solar system as regards planets, though there are plenty of retrograde comets.

The mass of Neptune has been variously estimated at

by

O. Struve; at 1880 by Peirce; at 1100 by Bond; at Too by Hind, from a combination of early measures; at is by the same from Lassell's Maltese measures; at Too by Littrow; at 1 by Mädler; and at os by Safford, which is the most recent evaluation.

039

The only known observations of Neptune made previously to its discovery in 1846 are two by Lalande, dated May 8 and 10, 1795, and one by Lamont of Oct. 25, 1845. Two by the same astronomer on Sept. 7 and 11, 1846, were probably due to Le Verrier's announcement made just before, and therefore are not entitled to be regarded as casual ones.

e Month. Not. R.A.S., vol. xv. p. 47. For some of Lassell's observations see vol. xii. p. 155, and vol. xiii. p. 37.

M

Owing to its immense distance, only Saturn and Uranus can be seen from Neptune. Though deprived of a view of the principal members of the solar system, the Neptunian astronomers, if there are any, are well circumstanced for inspecting comets, and are also able to take, probably with considerable success, observations on stellar parallax, seeing that they are in possession of a base-line of 5,500,000,000 miles, or one 30 times the length of that to which we are restricted.

Our present knowledge of the movements of Neptune is derived from the investigations of the late S. C. Walker, of Philadelphia, U. S., and the tables of M. Kowalski.

BOOK II.

ECLIPSES & THEIR ASSOCIATED

PHENOMENA.

CHAPTER I.

GENERAL OUTLINES.

Definitions.- Position of the Moon's orbit as regards the Earth's.- Consequences resulting from their being inclined.-Retrograde motion of the nodes of the Moon's orbit. Coincidence of 223 synodical periods with 19 synodical revolutions of the node.-Known as the "Saros."-Statement of Diogenes Laërtius.— Illustration of the use of the Saros.-Number of Eclipses which can occur.-Solar Eclipses more frequent than Lunar ones.—Duration of Annular and Total Eclipses of the Sun.

THES

HE phenomena which I am about to describe are those resulting from the interposition of celestial objects. We know well that inasmuch as many of the heavenly bodies are constantly in motion, the direction of lines drawn from one to another will vary from time to time; and it must occasionally happen that three will come into the same line. "When one of the extremes of the series of 3 bodies which thus assume a common direction is the Sun, the intermediate body deprives the other extreme body, either wholly or partially, of the illumination which it habitually receives. When one of the extremes is the Earth, the intermediate body intercepts, wholly or partially, the other extreme body from the view of observers situate at places on the Earth which are in the common line of direction, and the intermediate