C A S S I N I. 





from a family, which hat ranked among the senato- 

 n.tl famili.-t; of Sienna since the ti: mal Cas- 



sini, who was archbishop of that city in 1426. After 

 t lie early part of his education under a private 

 tutor, he was sent to tin of Jesuits at Genoa, 



where he made such a rapid progress in literature, that 

 gome of his Latin poems were published when he was 

 only eleven years of age. In consequence of some 

 books on judicial astrology having been lent to him by 

 an ecclesiastic, when he was on a visit at the country 

 house of M. Lercaro, the doge of Genoa, his atten- 

 tion was directed to the study of the heavens. He 

 began to predict future events from the aspects of the 

 heavenly bodies, and made numerous extracts from 

 the astrological books which were put into his hands ; 

 but having accidentally read the work of Pic de la 

 Mirandi against astrologers, he burned all the extracts 

 which he had made, and abandoned forever the dreams 

 of astrology. He now devoted himself wholly to astro- 

 nomy ; and such was the rapidity of his progress, that 

 in the year 1650, when he was only twenty-five years 

 of age, he was invited by the senate of Bologna to the 

 professorship of astronomy, which had been vacant 

 for several years by the death of Cavalleri ; a situa- 

 tion in which he continued for several years, devoting 

 the whole of his leisure time to astronomical obser- 

 vations. From a series of observations on the comet 

 of 1652, made with the Marquis of Mal vasia, who 

 had been instrumental in bringing him to Bologna, 

 he concluded that comets were not of a meteoric na- 

 ture as had been imagined, but that they were guid- 

 ed in their paths by the same laws as the planetary 

 bodies; and he explains the motion of the comet by 

 a circle described round the earth and beyond the 

 orbit of the moon. These observations were pub- 

 lished in his first production, which appeared in 

 1653, under the title of De Cometa anni 1652 et 

 1653. Muntinae, fol. In the same year he obtained 

 a solution of the celebrated problem for determining 

 geometrically from the mean and true place of a 

 planet, the eccentricity of its orbit, arid the place of 

 its apogee, which had baffled the ingenuity both of 

 Kepler and Bullialdus. In 1653, when the church 

 of St Petronius at Bologna underwent a repair, 

 Cassini obtained permission to draw the famous me- 

 ridian line, which we have already described in our 

 account of that city. This meridian line, which had 

 been first drawn in 1575 by Egnazio Dante, was re- 

 newed in 1695 by Cassini, when a full account of it 

 was published by him, entitled, La Meridiana del 

 tcmpio di 8. Pelronia, tirnta c preparata per IP. otser- 

 vationi attrnnomiche I' an no 1655, rivista c restatirata 

 I'anno 1695. Bologna, fol. In the year 1657, Cassi- 

 ni went to Rome in the capacity of assistant to the Mar- 

 quis Tanara, who had bfen sent by the senate of Bo- 

 logna as ambassador to Pope Alexander VI I. respect- 

 ing certain differences which had arisen between the ci- 

 ties of Bologna and Ferrara, about the inundation of 

 the Po ; and such was the skill and judgment which 

 he displayed on this occasion, that he was chosen su- 

 penntendant of the waters of the state of Bologna. 

 Mantis Chigi, the Pope's brother, afterwards ap- 

 pointed him in 1663, inspector general of the forti- 



fications of the castle of Urbino, and he was aUo 

 chosen engineer for all the rivers in the ecclesiastical 

 state. Cassini was employed in settling with M.Viviani 

 the diiiercnce which arose between Pope Alexander 

 V 1 1. and the Grand Duke of Tuscany, respecting the 

 waters of theChiana ; and such was the personal regard 

 which this pontifl entertained for him, that he fre- 

 quently sent for Cassini to converse with him upon 

 the sciences, and urged him, in vain, by the promises 

 of preferment, to enter into the church. 



During these occupations, which were rather fo- 

 reign to the habits of a practical astronomer, Cassini 

 found leisure to prosecute his favourite study. 

 observed almost all the celestial phenomena which 

 occurred, he discovered the rotation of Mars upon 

 his axis, and he formed tables of the motion of Ju- 

 piter's satellites. His various observations made in 

 his native country were published in the following 

 works : 



1. Specimen Observationum Bononicnsium 

 noctii verni, anni 1656. Bonon. 1H56, fol. 



'2. Pane figure intagliatc in rime, che repreaentano 

 la perspettiva di Pianeiti un le proporzione delle loro 

 di-itanze a I Sole et alia terra, periodiche revolution, 

 direzzioni e relrogradationi. Bonon. 1659. fol. 



3. EpistoliC Attronomicce cum tabnlis ad Marckion 

 Malvasiam inserts in cjusdem Malvasiee eptiemtridi- 

 bus. Muntiiiie, 1662. to.. 



4. Epistolce de obscrvalionibus in D. Pelronii templo 

 huhilis. Bonon 1663. fol. 



5. Osservatione de eclisse Solar e falta in Ferrara 

 anno 166'!-, con unajigurn intaglinta in rame, eke re- 

 presenla itno tiuovo methodo di irovar le apparcnze 

 varie che fa nel medesimo tempo in tutta la terra. 

 Ferrara, 1664-. fol. 



6. Theoria mot us Cometa anni 1664-. Romae, 1665. 



7. Lcllcre astronomicke al Signor Abbate Ottavio 

 Falconicri sopra il conjruitto di alcune osservazioni 

 delle comete dell' anno 1665. Romae, 1665. fol. 



8. Lctlere aslronomiche sopra Vombre de piancti 

 Medicei in Giove. 1665. Rom. fol. 



9. Quatro lettcre al Signor Abb. Falconieri, sopra 

 la varieta del macchie osier-cafe in Giove, e loro 

 diurne revoluzioni con le tavole. Rom. 1665. fol. 



10. P. Gottigniez et Joann. Dom. Cassini Epintolee 

 du.ce astronomical, de dijfficultatibus circa eclipses in 

 Jove a Mediceis planelis effectas, aliaque noriter in 

 ipso detecla. Bonon. 166*5. fol. 



11. * Dissertationes Attronomicae Apologeticce. 

 Bonon. 1665. fol. 



12. Epistola ad Geminianum Montanari de rrfrac- 

 tionum celcstittm methodo. Bonon. 1665. fol. 



13. Martis circa axem proprium revulubilis okser~ 

 vationes Bonomce habitis. Bonon. 1666 



14. De Solariltuf Hypothe^biu et Refract ionibus, 

 Epi<ttthc ties. Bonon. 1666, fol. 



15. Disceptaiio apologeiica de Maculis Jm<is ft 

 Murtis ann, 1666, 1667, et de conversions l\nerit 

 circa ajrem suam. 



16. Ephemerides Bononienses mcdiccorum siderum. 

 Bonon. 1668. 



17. Spina celeste, meteora osservala nell' anno 1668 

 in Bologna. Bonon. 1668. fol. 







This work contains, among other things, a dissertation on the spots of Mars and Jupiter, and a reply to two brothers ot 

 4 tie name of Serris, who maintained that Fontana had discorered the rotation of Mars* 



