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Researches respecting the New Planet Neptune.

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ART. VIII.-1. Recherches sur les mouvements d'Uranus. Par M. U. J. LE VERRIER.* Comptes Rendus, &c., Juin 1, 1846. Tom. xxii. p. 907.

2. Sur la Planète qui produit les anomalies observées dans le mouvement d'Uranus.-Détermination de sa masse, de son orbite, et de sa position actuelle. Par M. U. J. LE Verrier. Id. Id., 31 Août, 1846. Tom. xxiii. p. 428.

3. Sur la Planète qui produit les anomalies observées dans le mouvement d'Uranus. Cinquième et dernière partie, relative à la détermination de la position du plan de l'orbite. Par M.U.J. LE VERRIER. Id. Id., 5 Octobre, 1846. Tom. xxiii. p. 657. 4. Recherches sur les mouvements de la Planète Herschel (dite Uranus).† Par U. J. LE VERRIER. Dated 5 Octobre, 1846; and published in the Connaissance des Temps, pour l'an 1849. Additions, &c. p. 1-254.

5. Planète de M. Verrier. Par M. ARAGO. This Notice contains an account of the discovery of the planet at Berlin by M. Galle, on the 23d September, with observations by M. Arago. Comptes Rendus, &c., Tom. xxiii. p. 659-663.

6. Comparaison des observations de la nouvelle planète avec la Théorie déduite des perturbations d'Uranus. Par M. LE VERRIER. Id. Id., 19 Octobre, 1846. Tom. xxiii. p. 741.

7. Examen des remarques critiques et des questions de priorité que la découverte de M. LE VERRIER a soulevées. Par M. ARAGO. Id. Id. Id., p. 741-755. In this article Mr. Arago discusses the claims of Mr. Adams as advanced in the Athenæum by Sir John Herschel, Mr. Airy, and Mr. Challis.

8. On the newly discovered Planet. By M. ENCKE. Translated in the Lond. & Edin. Phil. Mag. for March 1847, vol. xxx. p. 181,-from the Berichten der Akad. der Wissenschaften zu Berlin, Oct. 22, 1846.

9. An explanation of the observed irregularities in the motion of Uranus, on the hypothesis of disturbances caused by a more distant planet, with a determination of the mass, orbit, and position

* On the 10th November, 1845, there appeared in the Comptes Rendus, &c. of that date, tom. xxi. p. 1050, an abstract of a Memoir by M. Le Verrier, entitled Première Mémoire sur la Théorie d'Uranus, but as it contains no reference whatever to the new Planet, we have not inserted it above.

In this Memoir, the planet is invariably called Uranus; but M. Le Verrier has added the following Note, in reference to his having adopted the name Herschel in the title of his Memoir :-" In my ulterior researches," says he, "I shall consider it as a strict duty to make the name Uranus completely disappear, and to call the planet only by the name of HERSCHEL. I regret extremely that the advanced state of the printing of this Memoir has not permitted me to conform to a resolution which I shall religiously observe in future.”—P. 1, Note,

of the disturbing body. By J. C. ADAMS, Esq., M.A., Fellow of St. John's College, Cambridge. Dated Nov. 12, 1846, and published in the Nautical Almanac for 1851. (See also Proceedings of the Astronomical Society, Nov. 13, 1846.) 10. Account of some circumstances historically connected with the discovery of the planet exterior to Uranus. By the ASTRONOMER-ROYAL. From the Proceedings of the Royal Astronomical Society, Nov. 13, 1846. Vol. vii. p. 121-145.

11. Account of observations at the Cambridge Observatory, for detecting the planet exterior to Uranus. By PROFESSOR CHALLIS, Id. Id., p. 145-149.

12. Special Report (to the Syndicate of the University of Cambridge) of Proceedings in the Observatory relative to the New Planet. By PROFESSOR CHALLIS. Dec. 12, 1846.

13. Second Report of Proceedings in the Observatory relating to the New Planet (Neptune.) By PROFESSOR CHALLIS. March 22, 1847.

THE writings enumerated in the preceding list contain the history and details of a discovery certainly the most remarkable in the Annals of Science. If the discovery of an Island or a Continent, on the little world which we inhabit, gives immortality to the adventurer who stumbles upon its shores, how shall we estimate the merit of the astronomer who detects a new planet amid myriads of stars, and extends more than a thousand millions of miles the limits of the system to which he belongs! This feat was performed when Sir W. Herschel added Uranus to the planets. The process, however, by which that discovery was made involved no exercise of sagacity, and demanded no effort of genius. A sharp eye, a good telescope, and a patient observer, are alone necessary to rescue a planet from the starry maze which conceals it; and we have in our own day witnessed these influences, in the discovery of the five small bodies which circulate between Mars and Jupiter.

To such discoveries, brilliant though they be, the triumph of astronomy which we are about to contemplate has no resemblance but in name. To detect a planet by the eye, or to track it to its place by the mind, are acts as incommensurable as those of muscular and intellectual power. Recumbent on his easy chair, the observer has but to look through the cleft in his revolving cupola, and number the beats of his clock, in order to trace the pilgrim star amid its companions, or, by the application of magnifying power, to expand its tiny disc, and thus transfer it to the planetary domains. The mathematician, on the other hand, has no such auxiliaries. He calculates at noon, when the stars disappear under a meridian sun. He computes at midnight, when

Respecting the New Planet Neptune.

209. clouds and darkness shroud the heavens; and from within that cerebral dome which has no opening heavenward, and no instrument but the eye of reason, he sees, in the agencies of an unseen planet, upon a planet by him equally unseen, the existence of the agent; and from the direction and amount of its action he computes its magnitude and place. If man ever sees otherwise than by the eye, it is when the clairvoyance of reason, piercing through screens of epidermis and walls of bone, grasps, amid the abstractions of number and quantity, those sublime realities which have eluded the keenest touch, and evaded the sharpest

eye.

Such indeed was the process by which a new planet has been added to the solar system; and, whether we consider the novelty of the subject, or the extraordinary discussions and proceedings to which it has given rise, we have no doubt that our readers will peruse with some interest the details of a discovery so remarkable, and of a controversy so strange.

So early as the year 1758, when the perturbations of Halley's Comet were the subject of discussion in the Academy of Sciences at Paris, the celebrated Clairaut hazarded the opinion, that bodies which traversed regions so remote might be influenced by forces wholly unknown, "such as the action of planets too distant to be discovered." This opinion, however, does not seem to have been adopted by astronomers, who found it an easier task to doubt the universality of the law of gravity, or to refer the irregularities in the motion of comets to the retarding influence of a luminiferous ether, than to sweep the heavens for new planets, or to deduce their existence, and determine their place, from the disturbances which they occasioned. An astronomer who had little faith in his own science, might have been permitted to question the extension of the law of gravity to the sidereal regions, or even to fill the boundless universe with a retarding medium; but science could not tolerate the heresy, that the law of solar attraction suffered a change beyond the orb of Saturn, and that a comet was guided towards its perihelion by a different law from that which caused it to pass its aphelion, and return to our system.

After the discovery of Uranus in 1781, astronomers were perplexed with the magnitude of the discrepancies between its observed and calculated places; but it was not till 1821, when Alexis Bouvard published his Tables of this planet, that these discrepancies, amounting sometimes to three minutes, attracted particular notice. The Rev. Mr. Hussey of Hayes in Kent, "having taken great pains with some observations of Uranus,' was led to examine closely Bouvard's Tables, and he then conceived "the possibility of some disturbing body beyond that planet." His first idea was "to ascertain some approximate place

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of this supposed body empirically, and then with his large Reflector to set to work and examine all the minute stars thereabouts;" but finding himself inadequate to the mathematical labour, he relinquished the matter altogether. A subsequent conversation with Bouvard in Paris, in 1834, rivetted his attention to the subject. The French astronomer, he found, had entertained similar views to his own, and had even been in correspondence with Hansen, who believed that one disturbing body would not account for the phenomena, and that there must therefore be two new planets beyond Uranus! Mr. Hussey's proposal to obtain the empirical places of the supposed planets, and to "sweep closely' for them, was so highly approved of by Bouvard, that he proposed to undertake the calculations, which he regarded as more laborious than difficult, and to transmit the results to Mr. Hussey, as "the basis of a very close and accurate sweep." M. Bouvard did not find leisure for an investigation of such magnitude, and Mr. Hussey, full of zeal and enthusiasm, applies to the Astronomer-Royal for his advice and assistance. In a letter, dated 17th November 1834, he communicates to Mr. Airy his own views, as well as those of Bouvard and Hansen, which we have already referred to, and he requests him, if he considers "the idea possible," to give him roughly the limits between which the planet— as he thought, or the planets, as Hansen thought—might be found during the ensuing winter. Mr. Hussey sagaciously adds, that as the inclination of the orbit might not be large, the zone to be examined would be comparatively inconsiderable; and he explains the very methods by which he expects to make the discovery-the very methods, too, by which the discovery has been since made: "I am disposed to think," says he, " that such is the perfection of my equatorial object-glass, that I could distinguish almost at once the difference of light of a small planet and a star. My plan of proceeding, however, would be very different: I should accurately map the whole space within the required limits, down to the minutest star I could discern; the interval of a single week would then enable me to ascertain any change." Had this noble proposal been embraced, as it ought to have been, the new planet might have been twelve years older than it is, and England might have enjoyed the undivided glory of its discovery. The views of the Astronomer-Royal were not in unison with those of Mr. Hussey, and, as if he had been born when Aquarius was in the ascendant, he throws cold water upon the glowing enthusiasm of his friend, and extinguishes for ever his well-founded expectation of adding to Apollo's lyre another string.

"

In his reply to Mr. Hussey he gives it as his opinion, without hesitation, that the subject (of the irregularities of Uranus) is not yet in such a state as to give the smallest hope of making

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out the nature of any external action upon Uranus." He adduces facts which he considers as indicating that there are no irregular perturbations in the motion of Uranus, and therefore "doubts the certainty of any extraneous action." But admitting the certainty of an extraneous action, "he doubts much the possibility of determining the place of a planet which produced it," and he is sure it could not be done till the nature of the irregularity was well determined from several successive revolutions,"* that is, till after the lapse of several hundred years!

In the year 1835, when the irregularities in the motion of Halley's Comet were ascribed by some astronomers to the resistance of the ether, M. Benjamin Valz, of Marseilles, wrote to M. Arago "that he would prefer having recourse to an invisible planet beyond Uranus. The revolution," he adds, "would, according to the law of distances, be at least triple that of the Comet, so that in every three oppositions, its perturbations would be reproduced, and the calculation of four or five intervals might enable us to recognise it. Would it not be admirable thus to ascertain the very existence of a body we cannot see!"†

Nearly three years after the defeat of Mr. Hussey's purpose, the Astronomer-Royal is again roused from his slumbers. M. Eugene Bouvard, the nephew of Alexis, announces to him, on the 6th October, 1837, his intention to reconstruct the tables of Uranus, and requests his opinion and aid. Finding that the differences in latitude between the observed and tabular places of the planet are continually increasing, he asks the question,"Does not this difference arise from an unknown perturbation introduced into the motions of this star by a body situated beyond it?" "I know not," he adds; "but this at any rate was my uncle's idea. I regard the solution of this problem as very important; but in order to succeed I require to reduce the observations with the greatest precision, and the means of doing this are often wanting."

* In making an apology for this last sentence, Mr. Airy states that " he thinks it likely that the same difficulty would still have been felt if the theorists (Adams and Le Verrier, we presume) who entered seriously upon the explanation of the perturbations had not trusted more confidently to Bode's law of distances than he did himself.” In this opinion we cannot concur. If Bode's law had never been heard of, the "theorists" would, in all probability, have assumed a mean distance for their planet much nearer the truth than Bode's law made it. They could not do otherwise than assume a distance conformable to existing analogies. For example, taking the mean distances of Jupiter, Saturn, and Uranus, as 52, 95, and 190, that of the earth being 10, then since 191 is just double of 95, the probable distance of the new planet might have been assumed as 380, which was done, or taking the ratio of 52 to 95 we should have 34-7, which is still nearer the true distance. A still closer approximation to the true distance of the new planet would have been obtained from the ratio of the distances of the planets nearer the sun, so that the theorists have been misled by Bode's law rather than benefited by trusting to it too confidently, and more than the Astronomer-Royal did.

+ Comptes Rendus, &c., tom. i. p. 130, and tom, xxiv. p. 35.

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