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ASTRONOMY.

ing some decayed universities, founding a new one in Vienna ;and causing the works of Aristotle, and Ptolemy’s Almagest , to betranslated into Latin. Two years after this, John de Sacro Bosco ,that is of Halifax, compiled from Ptolemy , Albategnius, Alferga-nus, and otiier Arabic astronomers, his work “ De Spinera,” whichwas held in the greatest estimation for 300 years after, and washonoured with commentaries by Clavius and other learned men.

(17.) In 1240, Alphonso, king of Castile, not only cultivatedastronomy himself, but greatly encouraged others; and by theassistance of several learned men corrected the tables of Ptolemy ,and composed those which were denominated from him the Alphon-sine Tables. About the same time, Boger Bacon, an English monk, wrote several tracts relative to astronomy, particularly ofthe lunar aspects, the solar rays, and the places ofthe fixed stars:and about 1270, Vitello, a Polander, composed a treatise on op-tics, in wdiich he shewed the use of refractions in astronomy.

(18.) Till the time of l’urbach, who was born in 1423, littlefarther improvement was made. lie constructed spheres andglobes, and wrote several astronomical tracts. In his solar tables,he placed the sun’s apogee in the beginning of Cancer ; butretained the obliquity of the ecliptic 23 !) 33as determined bythe latest observations. lie also observed some eclipses, madenew tables for computing them, and had just finished a' theory ofthe planets, when he died in 1462, being only 39 years of age.

(19.) Purbach was succeeded in these labours by his pupil andfriend, John Muller, commonly called Regiomontanus , He com-pleted an epitome of Ptolemy ’s Almagest, wdiich Purbach had be-gun, and made several instruments for astronomical observations,among which was an armillary astrolabe, like that used at Alexandriaby Hipparchus and Ptolemy , with which and a good clock, thenbut a late invention, he made many observations. He composedepheinerides for 30 years to come, shewing the lunations, eclipses,&c. ; printed the works of many of the most celebrated ancientastronomers, and wrote a theory of the Planets and Comets.After Muller’s death, which happened at Rome in 1476, in his40th year, Bernard Walther collected his papers, and continuedthe astronomical observations till his own death. The observa-tions of both were collected by order of the senate of Nuremberg ,and published there in 1544, by John Schoner.

(2 >.) Walther was succeeded, as astronomer at Nuremberg , byJohn Werner, a clergyman, who, by comparing his own observa-tions, made in 1514, with those of his predecessors shewed thatthe motion of the fixed stars, since called the precession of theequinoxes, is 1° 10’ in 100 years, lie made also the first star ofAries 26° distant from the equinoctial point, and the obliquity oftire ecliptic only 23° 2S'; and published a translation of Ptolemy’sGeography , with a commentary, in which he first proposed themethod of finding the longitude at sea by observing the moon’sdistance from the fixed stars. Werner died in 1528, aged 60.

(21.) Nicolaus Copernicus rose about this time, and made sogreat a figure in astronomy, that the true system, discovered, orfather renewed, by him, has been eversince stiled the Copernican.He restored tjie old Pythagorean system of the world, which Ladbeen set aside from the time of Ptolemy . About A. D. 1507, heconceived doubts of the Ptolemaic system, and entertained no-tions about the true one, which he gradually improved by aseries of astronomical observations, and the study of former au-thors. By these he formed new tables, and completed his workin 1530, containing a renovation of the true system of the uni-verse, in which all the planets are considered as revolving aboutthe sun. The work was printed in 1543, under the care of Scho-ner and Osiander, by the title of “ Revolutiones Orbium Coelesti-um;” and the author received a copy of it a few hours before hisdeath, on the 23rd of May 1543, he being then 70 years of age.

(22.) After the death of this great luminary of Astronomy , thescience and practice of it were greatly improved by Schoner,Nonius, Appian, Gemma Frisius, Rothman, Byrgius,’the Land-grave of Hesse , Ac. And in 1571, William IV. Landgrave ofHesse Cassel, applied himself to the study of astronomv, about A.D. 1561 ; and with the best instruments which could then be pro-cured, made a great number of observations, published by Spel-lius in 1617, and preferred by IIevelius to those of Tycho Brahe .From these observations he formed a catalogue of 400 stats, withtheir latitudes and longitudes, adapted to the beginning of the year1593. Tycho Brahe, a Danish nobleman , discovered a new stat-in the chair of Cassiopeia; this induced him, like Hipparchus on

a similar occasion, to make a new catalogue of the stars; whichhe composed to the number of 777, and adapted their places tothe year 1600. He also made a great number of observations onthe sun, moon, and planets, and was the first who made allowancefor refraction in his calculations. Tycho was the inventor of asystem of astronomy, a kind of Semi-Ptolemaic, which he vainlyendeavoured to establish instead of the Copernican. Ilis nume-rous works however, shew that he was a man of great abilities;and his discoveries, together with those of Purbach and Regiomon-tanus , were collected and published together in 1621, by Longo-montanus, the favourite disciple of Tycho.

(23.) After Tycho’s death, which happened in 1601, Kepler rendered uncommon service to astronomy, lie discovered thatall the planets revolve about the sun, not in circular, but inelliptical orbits, having the sun in one of the foci of the ellipse;that their motions arc not equable, but varying, quicker or sloweras they are nearer to the sun, or farther from him ; that the areas de-scribed by the variable line drawn from the planet to the sun, areequal in equal times, and always proportional to the times ofdescribing them ; and that the cubes of the distances of the planetsfrom the sun, are in the same proportion as the squares of theirperiodical times of revolution. By observations also on comets,he concluded, that they are freely carried about among Ihe orbitsof the planets in paths that are nearly rectilinear, hut which hecould not then determine. Kepler likewise speaks of gravity asa power mutual between all bodies, and that the tides arise Iromthe gravitv ofthe waters towards the moon.

(24.) At this time tiiere were many other good proficients in astro-nomy ; as Wright, Napier, Bayer, Ac. Wright made severalgood meridional observations of the sun, with a quadrant of sixteet radius, in the years 1594, 1595, and 1596; from which hegreatly improved the theory of the sun’s motion, and computedmore accurately' his declination, than any person had done before.In 1599, he published also an excellent work, entitled, “Certain.Errors in Navigation discovered and detected,” containing a me-thod which has commonly, though erroneously, been ascribed toMercator . To Napier we owe some excellent theorems and im-irovements in spherics, besides the ever-memorable invention ofogarithms. Bayer, a German, published his Uranometria, or thefigures of all the constellations visible in Europe , with the starsmarked on them, and accompanied by names, or the letters oftheGreek alphabet; a contrivance by which they may easily be re-ferred to -with distinctness and precision.

(25.) About the same time, astronomy was cultivated abroadby Mercator , Maurolycus, Magimis, Ilomelius, Schultet, Stevin,Galileo, &c. and in England by Thomas and Leonard Digges ,John Dee , Robert flood, Harriot, &c. The beginning ot the17th century was particularly distinguished by the invention oftelescopes, and the application ot them to astronomical observa-tions. 'fbe more distinguished early observations with the teles-cope were made by Galileo, Harriot, Huygens , Hook, Cassini,See. It is said that, from report only, Galileo made for himselftelescopes, by which he discovered inequalities in the moon’s sur-face, Jupiter’s satellites, and the ring of Saturn ; also spots on thesun, by which he found out the revolution of that luminary on itsaxis; and he discovered that the nebula; and milky way were fullof small stars.

(26.) Mr. Harriot, who had previously been known only as analgebraist, made much the same discoveries as Galileo , and asearly, if not more so, as appears by bis papers not yet printed, inthe possession of the Earl ot Egremont. And Mr. I lorrox, a youngastronomer of great talents, found out in 1633, that the planetVenus would pass over the sun’s disk on the 24th of November,1639, O. S. an event which he announced only to his friend Crab-tree ; and these two were the only persons in the world that observedthis transit. Ilorrox made also many other useful observations,and had even formed a new theory of the moon, taken notice ofby Newton; but his early death, in the beginning of 1640, puta stop to his usetul and valuable labours. Ilevelius, Burgomastirof Dantzic, contemporary of Dr. Hook, flourished about the sametime, and observed the spots and phases of the moon ; from whichobservations, he compiled bis Selenographia. An account of hisapparatus is contained in his work entitled “ Machina Cceleslis,” abook now very scarce, as most of the copies were accidentallyburnt, with the whole house and apparatus, in 1679.—Ileveliusdied in 1688, aged 76.

6 (27.) Iluygens