AST 



AST 



vallies and mountains. The fun, which had generplly been 

 confidcred as a globe of pure fire, was obfcrved to be fiillied 

 bv a number of dark fpots, which appeared on various parts 

 of his furface. A gr^at number of new liars were difco- 

 vered in every part of the heavens ; the planet Jupiter was 

 found to be attended with four moons, which moved round 

 him in the fame manner that our moon moves round the 

 earth ; the phafcs of Venus appeared like thofe of the 

 moon, as had before been concluded by Copernicus from his 

 theory; and in fliort, moft of the obfervations he made 

 furnillied new proofs of the truth of the Copernican fyilem. 



In publifiiing the difcoveries which lie had made with this 

 new inllrument, Galiko fliewed in the moll ineontellible 

 manner, the annual and diurnal motion of the earth; which 

 doftrinc, however, was thought fo alarming, that it was 

 immediately declared heretical, by a congregation of cardi- 

 nals, who Wire affembled upon the occalion ; and its vene- 

 rable author, one of the moft virtuous and enlightened men 

 of his age, was obliged to abjure, upon his knees, and in 

 the moll lolemn manner, a truth, which nature and his own 

 underftanding had ihewn him to be incontrovertible. After 

 this, he was condemned to perpetual imprifonment; from 

 which, however, at the end of a year, he was enlarged, by 

 the folicitations of the grand duke ; but, that he might 

 not withdraw hinifelf from the power of the inquifition, he 

 was forbid to quit the territory of Florence, where he died 

 in 1642 ; c;i:rying with him the regrets of Europe, enhght- 

 ened by his labours, and their indignation againft the odious 

 tribunal which had treated him fo unworthily. For the oath 

 of abjuration, and further particulars of this-tranfaftion, 

 fee Bonnycaftle's Ailronomy, p.ioi. 3d edit, and the article 

 Galileo in this work. 



The celebrated Harriot alfo, who has hitherto been 

 known only as an jlgebraili, made, much about the fame 

 time, fimilar difcoveries with thofe of Galileo, as appears 

 by his papers not yet printed, which are in the poireflion of 

 the earl of Egremont. Mr. Horrox, likeuife, a young 

 aftronomer of great merit, about this time, deferves to be 

 mentioned, on account of his obfervation of the tranlit of 

 Venus over the fim's dilk (fee Transit), on the 2.|.th of 

 November 1639 ; which event he announced to his friend 

 Mr. Crabtree; and thefe two together had the fingular fatis- 

 faftion of witnefilng, for the firll time, a phenomenon which 

 had never before been fcen by human eyes. Horrox had 

 even formed a new theory of tlie moon, which is taken 

 notice of by Newton ; but his early death, which liappened 

 in the beginning of .the year 1 64c, put a Hop to his ufcful 

 labours. 



The ilifcoveries of Huvgens fucceeded thofe of Kepler 

 and Galileo ; and few men have, perhaps, merited more of 

 the fcienccs, by the importance and fubhinity of his re- 

 fearches. Among other things, his happy application of the 

 pendulum to clocks, is one of the moll advantageous pre- 

 Icnts that v/as ever made to aftronomy. He was alfo the 

 firll who found that the fingular appearances of Saturn, are 

 produced by a ring, by which the planet is furrounded ; and 

 his afiiduity in obferving it, led him to the difcovery of one 

 of its fatellites. Geometry, mechanics, and optics, are alfD 

 indebted to him for a great number of difcoveries : and if this 

 rare genius had had the idea of combining his theorenw on 

 centrifugal forces, with his inquiries into the devclopenient 

 of curves, and- the laws of Kepler, he would have raviflicd 

 from Newton his theory of curvilinear motions, and that of 

 gravitation ; but thefe are the things in which difcoveries 

 generally confill. 



Next to Huygens, may be mentioned Hevelius, a burgo- 

 mailcr of Danuic, who rendered hinifelf highly ufeful to 



aflronomy by Ills numerous and immenfe labours: few ob- 

 fervcrs having ever exiilcd who were more indefatigable. It 

 is to be lamented, however, that he refufed to make ufe of 

 inllruments with tcltfcopic fights, an invention introduced 

 about that time by the celebrated Dr. Hook, and which 

 gave a prccifion to obfervations unknown to former aftrono- 

 mers. He even contefted their utility, ar.d a warm difpute 

 having arifcn between him and Dr. Hook itpon this fubjecl. 

 Dr. Halley, then a young man rifing fall into fame and emi- 

 nence, was fent to examine his inftruraents, which were 

 found to be excellent of their kind. The two aftronomer* 

 made feveral obfer\-ations together, much to their fatisfac- 

 tion; and among them was one of an occultation of Jupiter 

 by the moon, by which they determined the diameter of the 

 latter to be 30' 33". 



About this epoch, aftronomy began to be more generally 

 cultivated and improved, in confequenccof the ellablilhment 

 of feveral learned focieties, which, by exciting a fpirit of 

 emulation and enterprife among their members, greatly con- 

 tnbuted to the advancement of every branch of the mathe- 

 matical and phyfical fciences. The chief of thefe were the 

 Royal Society of London, and that of the Academy of 

 •Sciences of Paris ; both of which have rendered great fer- 

 vices to aftronomy, as well by the eminent men they have 

 produced, as by the zeal and ardour with which the fciencc 

 has conftantly been promoted by them. One of the firll 

 effects produced by thefe ellablifliments, was the great im- 

 provement of telefcopes and other inllruments, which had 

 hitherto been too much neglecfted for want of proper encou- 

 ragement. Huvgens conllruftcd a tclefcope of 123 feet ; 

 with which he long obfer^-ed the moon and planets, and wa« 

 the firll that difcovered Saturn's ring. The celebrated Caf- 

 fini alfo employed inftruments of this kind, of 200 and 3CO 

 feet focus, with which he faw the five fateUites of Saturn, 

 with his zones or belts, as well as the (hadows of Jupiter's 

 fatellites paffing over his body. 



The length of refrafting telefcopes, however, was ftill a 

 great inconvenience; to remedy which, as well as the great 

 aberration of their rays, Merfennus is faid to have firll 

 ftarted the idea of making telefcopes with reflectors, inftead 

 of lenfes, in a letter to Defcartes ; and in 1663, James Gre- 

 gory of Aberdeen, (hewed how futh an inftrument might 

 be conllrucled. Newton, alfo, after fpending fome time 

 on the conllruction of both thefe forts of telefcopes, dif- 

 covered the great inconvenience which arifes to rcfradlors, 

 from the diflerent refrangibility of the rays of light, and 

 therefore purfuing the other kind, he prefentcd in the year 

 1672, to the Royal Society, two reflectors, with fpherical 

 fpecula, as he could not then contrive the means of giving 

 tl'.cm a paiabolic figure. It is proper to obferve, however, 

 that the defects of refraifling tehfcopes, arifing from the 

 different refrangibility of the rays of light, have fiuce been 

 completely obviated by the ingenious Mr. DoUond. See 

 Achromatic Tklescope. 



Towards the latter part of the feventeenth century, and 

 the beginiMng of the eighteenth, praftical aftronomy feems 

 rather to have languiflied; but at the fame lime, the theoreti- 

 cal part was carried to the liigheil degree of pcrfeilion, by the 

 immortal Newton in his" Principia," and by the aftronomy 

 of David Gre^rory. (See Newtonian Philosophy.) About 

 this time alfo, clock and watch-work was greatly improved 

 bv Mr. Graham, who likewife conftrudled the old eight 

 feet mural arch at the Royal Obfervatory at Greenwich, 

 and the zenith feflor of twenty-four feet radius, with which 

 Dr. Bradley difcovered the aberration of the fixed ftars. (See 

 AiiERRATioN.) The rcfleding telefcope of Gregory and 

 Ncwtou, was alfo greatly improved by Mr. Hadley ; but 



who 



