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HISTORY OF PHYSICAL ASTRONOMY.

CHAPTER XII.

Introductory Remarks.—Ancient Observations of Uranus . — Calculation of Tables of thePlanet by Delambre.—Tablesof Bouvard.—Irregularities of the Planet.—Speculationsrespecting their Origin.—Errors of Radius Vector.—Researches of Geometers.—Bessel.— Adams.—Inverse Problem of Perturbation.—Account of Adams’ Researches relativeto the existence of a Planet exterior to Uranus. —Results obtained by him.—Researches

of the French Astronomers on the Theory of Urflfcus. — Eugene Bouvard_Le Verrier.

—Account of his Researches_Near agreement of his Results with those of Adams.—

Steps taken by Airy and Challis for the purpose of discovering the Planet.—NewResults obtained by Adams.—Explanation of errors of Radius Vector. — Account ofthe second part of Le Vender's Researches on the Trans-Uranian Planet. — Address ofSir John Herschel at Southampton.—The Planet discovered at Berlin by Galle.—Admiration excited by the Discovery.— Account of Challis’ Labours.—Public An-nouncement of Adams’ Researches.—Impression produced by it.—Historical Statementof the Astronomer Royal.—Publication of the Researches of Le Verrier and Adams.—Remarks suggested by the Discovery of the Planet.

Thf. Theory of Gravitation is not more remarkable for the sublimity of itsresults than for its varied and effective character, when considered as aninstrument applicable to the discovery of truth. By unfolding its prin-ciples, the astronomer, without leaving his observatory, has been enabledto determine the distances of the sun and moon from the earth, to weighthe planets as in a balance, and to educe order and stability from thecountless irregularities of their motions. It has conducted him to a know-ledge of the figure of the earth by merely watching the motion of the moonor the swinging of a pendulum, and it supplies the means of ascertainingthe figures of the celestial orbs without measuring their apparent dimen-sions. The eccentric aberrations of comets, the ebbing and flowingof the tides, and the oscillations of the atmosphere, all equally attest thevalue of its guidance in exploring the hidden operations of nature. But astill more striking triumph of this magnificent theory vvas reserved for ourown day, when the mathematician, by meditating in his chamber upon itsprinciples, has succeeded in revealing the existence of a new planetaryworld, vastly exceeding the earth in magnitude, which had hitherto escapedthe scrutinies of astronomers, aided by all the powerful appliances of opticalscience.

Soon after the discovery of Uranus by Sir William Herschel in 1781, itwas ascertained that astronomers had observed it on many previous occa-sions without recognising it to be a planet. Even as early as 1690, Flam-stead had designated it as a star of the sixth magnitude; and from that year,down to 1781, astronomers had determined its position no fewer thannineteen different times, under an erroneous impression of its real nature*.

* Bode first discovered two ancient observations of Uranus ; one in the Historia Celestisof Flamstead (the observation of 1690), and the other in one of Mayer’s Catalogues. Soonafterwards Lemonnier detected three positions of the planet among his own observations.Bessel, while engaged in reducing Bradley’s observations, found that the position of Uranus