It was about this period that the question respecting the figure of the earth appears to have been satisfactorily decided, and in favour of Newton's theory. M. Cassini concluded, from the measurement of M. Picard, that it was an oblong, spheroid, but Sir Isaac Newton, from a consideration ofthe laws of gravity, and the diurnal motion of the earthy had determin ed its figure to be that of an oblate spheroid flattened at the poles, and protuberant at the equator. To determine this point Louis XI". ordered two deerees of the meridian to be measured, one under or near the equator, the other as near as possible to the poles; the ex pedition to thenorth beingintrusted to Messrs. Manpertnis and Clairaut, that to the south to Messrs. Condamine, Bougeier, and Don Ulloa. Among the many observations made by those who went on this expedition, it was found by those who went to the south that the attraction of the mountain of Peru had a sensible effect on the plumb lines of their large instruments, which is supposed to afford an experimental proof of the Newtonian doctrine of gravitation. A similar observation has since been made by Dr. Maskelyne on the mountain Schehallien in Scotland.
The eighteenth seamy was marked by the discoveries of Dr. Bradley, the successor to Dr. Halley as Astronomer Royal, and Dr. Herschel, who also filled the same post so honourably to himself. Dr. Bradley discover ed the aberration of light, and the notation of the earth's axis, besides having formed new and accurate tables of the motions of Jupiter's satellites, and the most correct table of refrac tions that is extant: alsowith a large transit in strument, and a new mural quadrant of eight feet radius, he made observations for determin ing the plares of all the stars in the Britishcata logue, and likewise nearly a hundred and fifty places of the moon. Dr. Herschel, byaugment
mg powers ofthe teleseope beyond any thing existing before, or even thought of in discovering a new planet, which he named .he Georgium Sides ; he also discovered two additional satellites to Saturn, besides those his own planet Among those who cultivated the higher branches of the science, and dis tinguished themselves by their rewanehes, Dr. ; Maskelyne, the predecessor of Dr. Herschel, who the foremost, luring been the origina tor of the Nautical Akaamwk, and breeteht into use the lunar method of determining the longitude, ikc.. besides making the requisite tables. The theoretical part of the science was indebted to Clairaut, Euler, Simpson, de la Cagle, Set, Gregory, Leadbetter, for many correct observations and elucidations. The practical part acquired a systematic form and many improvements from the pens of Lalonde, Ferguson, Emerson, Bonnycanle, Vince, historians of the science are Weilder, in his History of Astronomy ; Baillie, in his History of Ancient and Modem Astronomy; Mootuccia, in his Histoire des Mathematimass; and Lalonde, in the first volume of his As tronomy.
The nineteenth century was commenced with the discovery of several new planets, namely, one in 1801 by M. Piazai of Palermo, named Ceres, between Mars and Jupiter; an other, named Pallas, discovered March 23, 1802, bv Dr. Olbers, of Bremen • a third, named Juno, by Mr. Harding, at die observe', Itory at Lilienthal, near Bremen, Sept. 1,1804; and a fourth, named Vesta, by Dr. Olbers, March 29, 1S07. These three last have also bee,observed to revolve between Mars and Jupiter.