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pretended to do more than give some examples of the historical progress of this subject, and shall not presume to carry the account further than I have already done.

I do not deviate from my original plan in thus limiting my narrative. For, as was formerly stated, the main object of the work was to present such a survey of the advances already made in physical knowledge, and of the mode in which they have been made, as might serve as a real and firm basis for our speculations concerning the progress of human knowledge, and the processes by which sciences are formed. And an attempt to frame such speculations on this basis was made in the Philosophy of the Inductive Sciences, which was published shortly after this History. To that work I must refer, for a further explanation of any views respecting the nature and progress of science which may here appear defective or obscure. intention to prepare for the press a new edition of the work, as soon as I shall have finished the preparation of the present publication.

I add a Postscript, containing a notice of a few points in the history of science which have come into view during the printing of the following pages.

It is my

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POSTSCRIPT TO THE SECOND EDITION.

(1). The planet exterior to Uranus, of which the existence was inferred by M. Le Verrier and Mr. Adams from the motions of Uranus (vol. 11. Note (L)), has since been discovered. This confirmation of calculations founded upon the doctrine of universal gravitation, may be looked upon as the most remarkable event of the kind since the return of Halley’s comet in 1757; and in some respects, as a more striking event even than that; inasmuch as the new planet had never been seen at all, and was discovered by mathematicians entirely by their feeling of its influence, which they perceived through the organ of mathematical calculation.

There can be no doubt that to M. Le Verrier belongs the glory of having first published a prediction of the place and appearance of the new planet, and of having thus occasioned its discovery by astronomical observers. M. Le Verrier's first prediction was published in the Comptes Rendus de l’Acad. des Sciences, for June 1, 1846, (not Jan. 1, as erroneously printed in my Note.) A subsequent paper on the subject was read Aug. 31. The planet was seen by M. Le Galle, at the Observatory of Berlin, on September 23, on which day he had received an

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express application from M. Le Verrier, recommending him to endeavour to recognize the stranger by its having a visible disk. Professor Challis, at the Observatory of Cambridge, was looking out for the new planet from July 29, and saw it on Aug. 4, and again on Aug. 12, but without recognizing it, in consequence of his plan of not comparing his observations till he had accumulated a greater number of them. On Sept. 29, having read for the first time M. Le Verrier's second paper, he altered his plan, and paid attention to the physical appearance rather than the position of the star. On that very evening, not having then heard of M. Le Galle’s discovery, he singled out the star by its seeming to have a disk.

M. Le Verrier's mode of discussing the circumstances of Uranus's motion, and inferring the new planet from these circumstances, is in the highest degree sagacious and masterly. Justice to him cannot require that the contemporaneous, though unpublished, labours of Mr. Adams of St. John's College, Cambridge, should not also be recorded. Mr. Adams made his first calculations to account for the anomalies in the motion of Uranus, on the hypothesis of a more distant planet, in 1843. At

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Mr. Adams informs me that as early as 1841 he conjectured the existence of a planet exterior to Uranus, and recorded in a

first he had not taken into account the earlier Greenwich observations; but these were supplied to him by the Astronomer Royal, in 1844. In September, 1845, Mr. Adams communicated to Prof. Challis values of the elements of the supposed disturbing body; namely, its mean distance, mean longitude at a given epoch, longitude of perihelion, eccentricity of orbit, and mass. In the next month, he communicated to the Astronomer Royal values of the same elements, somewhat corrected. The note, p. 306, vol. II., of the present work, in which the names of MM. Le Verrier and Adams are mentioned in conjunction, was in the press in August, 1846, a month before the planet was seen. As I have stated in the text, Mr. Adams and M. Le Verrier assigned to the unseen planet nearly the same position; they also assigned to it nearly the same mass; namely, 21 times the mass of Uranus. And hence, supposing the density to be not greater than that of Uranus, it followed that the visible diameter

memorandum his design of examining its effect : but deferred the calculation till he had completed his preparation for his examintion in January 1843. He was the Senior Wrangler on that occasion. The conjecture of an exterior planet was not quite

It had occurred to Mr. Hussey, M. Alexis Bouvard, and and M. Hansen, as early as 1834. See Mr. Airy's Account read to the Royal Astronomical Society, Nov. 13, 1846.

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would be about 3", an apparent magnitude not much smaller than Uranus himself.

M. Le Verrier has mentioned for the new planet the name Neptunus; and probably, deference to his authority as its discoverer will obtain general currency for this name.

(2). To the account of Tables of the Sun, Moon, and Planets, given vol. II. p. 304, I may add a notice of an important volume recently published; Reductions of the Observations of Planets made at the Royal Observatory, Greenwich, from 1750 to 1830, (1845). These Reductions were made under the superintendence of the Astronomer Royal, the computations being executed by order of the Lords of the Treasury, and published by order of the Lords of the Admiralty. The volume contains the observations reduced and compared with Lindenau's Tables of Mercury, Venus, and Mars, and with Bouvard's Tables of Jupiter, Saturn, and Uranus. The object of the work is stated to be (Introd. p. xxx.) “the comparison of a long series of observed places with theoretical places, computed by means of the same fundamental elements (duly corrected for perturbation) throughout.” The ultimate end contemplated by such a work is the correction of the fundamental elements of the planetary motions.

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