(504 CAS 



CiMini, 18. Nova ratio inveniendi mctrice et directe apo- 

 John. p. g(7> excentridtates, et anomalias motus planetarum. 

 ^r-** Bonon. 1669. 



Cassini'e tables of Jupiter's satellites having acci- 

 dentally fallen into the hands of the celebrated French 

 astronomer M. Picard, he conceived a high opinion 

 of the abilities of their author ; and such was the fame 

 which that work acquired, that Louis XIV. was anxi- 

 ous to number him among the members of the French 

 academy. Cassini, however, declined the invitation, 

 which was transmitted to him, unless the consent of 

 his superiors was obtained ; and Pope Clement IX. and 

 the senate of Bologna having yielded to the solicita- 

 tions of the French king, Cassini was granted leave of 

 absence for six years. In the beginning of the year 

 166'9 he came to Paris, and in the same year he was 

 appointed astronomer royal, and was admitted a pen- 

 sioner of the academy. When his time of absence was 

 about to expire, the Pope and the senate of Bologna 

 insisted upon his return on pain of forfeiting all his 

 emoluments and revenues, which he had hitherto been 

 permitted to enjoy. The minister Colbert induced 

 him to remain, and in the year 1673 he was natu- 

 ralized, and entered into the married state. 



The completion of the royal observatory in 1670, 

 enabled Cassini to devote himself, without interrup- 

 tion, to practical astronomy. In September 1671, 

 he began his laborious career, and during the period 

 of 41 years he made more observations than was per- 

 haps ever done by any individual astronomer. These 

 observations are recorded in no fewer than 165 me- 

 moirs, with which he enriched the Memoirs of the 

 Academy of Sciences, and they contributed greatly to 

 extend the science of astronomy. Cassini made a set 

 of regular observations on the equinoxes and solstices, 

 and on the oppositions and conjunctions of the pla- 

 nets. On the 5th of October 1671, he discovered the 

 fifth satellite of Saturn ; on the 23d December 1672 

 he discovered the third ; and in the month of March 

 1681, he discovered the first and second satellites of 

 the same planet. He had the merit also of discover- 

 ing the rotation of the fifth satellite, the belts of Sa- 

 turn and Jupiter, the spheroidal figure of Jupiter, 

 the zodiacal light, and he was the first who gave a 

 satisfactory theory of the moon's libration. 



In the year 1695, Cassini undertook a journey to 

 Bologna in company with his son, for the purpose of 

 examining the meridian line in the church of St Pe- 

 t robins, which he had drawn in 1655, and he found 

 that it had not sustained any variation in the course 

 of 40 years. In 1700, he continued, to the very south 

 of France, the meridian line which Picard had begun, 

 and he published an account of the undertaking in 

 the Memoirs of the Academy fur 1701, under the ti- 

 tle of DC la Meridienne dc I' Observatoire Roy ale, pro- 

 longeejusqu'aux Pyrenees. In the latter part of his 

 fife Cassini lost his sight, and he died without any 

 disease on the 14th of September 17 12, at the advan- 

 ced age of 87. He had lost his eldest son at the bat- 

 tle of La Hogue ; and he was succeeded in the ob- 

 servatory and in the academy by his youngest son, 

 the subject of the following article. 



Besides the works which Cassini printed in Ita- 

 ly, and the 165 memoirs on astronomical subjects, 

 he published the following 1 1 memoirs on general 

 subjects : 1. Observations sur la Manieredefaire de 



S I N I. 



puits, et des jets d'Eau a Moclene. Mem. Acad. Cawlni 

 1666, torn. i. 2. Sur la Balance Arilhmetiquc. Id. Jaraes 

 p. 142. 3. Sur un Nouvclle Progression des Norn- "~~^~~ 

 bres. Id. p. 20 1 . 4-. Sur un Eau renjermve dans un 

 Bouteille, et quifumoit coiitiiiuetlement u'es qn'on en 

 otoit le bouchon. Id. p. 212. 5. Sur la quantiic 

 d'Eau necessaire pour faire d'aller un moulin. Id. p. 

 286. 6. Sur un Meteore en forme de Globe dejeu 

 de la grandeur de la Lune, vu en 1687. Id. torn. ii. 

 p. 19. 7- Sur la Figure de la Neige. Id. p. 87. 8. 

 Stir I'Emptioii du Vemve en 1694. Id. p. 127. 9. DC 

 la Figure de la Neige. Tom. x. p. 25. 10. Sur dc 

 Parhelies vues en Janvier 1693. Id. torn. ii. p. 10;!. 

 11. Sur un Balance Arithmetique. Machin. Approuv. 

 Tom. i. p. 143. Caasini also made many observa- 

 tions on insects, addressed to M. Montalbani, who 

 published them in the works of Aldrovandus. He 

 likewise made a number of experiments on the trans- 

 fusion of blood. 



Cassini published also the following separate 

 works. Nouvelles Observations des laches du Soldi ', 

 avec quelques autres Observations sur la Salurne. 

 Paris, 1671, 4to. Observations et Reflexions sur hi 

 Comete de 1672. Decouvertes de deux nouvellea 

 Planetes autour de Saturne. Paris, 1673, fol. Obser- 

 vations et Reflexions sur la Comele de 1680 et 1681. 

 Paris, 1681, 4to. Nouvelles decouverles dans le Globe 

 de Jupiter. Paris, 1690, 4to. 



The following works were left unfinished, or in 

 MS. Nuncii Siderei Interpret. Magna periodus lu- 

 nisolaris et Paschalis duobus libris compre/iensa, quo- 

 rum primus magnce periodi fundamenta ejusque usum 

 exponit, alter usum ejus cimlem et ecclesiasticum. Una 

 Cosmographie ou une description du Monde; en vers 

 Italien. Tables des Mouvemens du Soleil et dc la 

 Lune. (o) 



CASSINI, JAMES, a celebrated astronomer, was 

 the youngest son of John Dominique Cassini, and was 

 born at Paris on the 18th of February 16'77. After 

 having finished his studies in his father's house, un- 

 der the care of M. Chazelle of the Academy of Sci- 

 ences, he was sent to study philosophy at the Ma- 

 zarin College under the celebrated Varignon, who was 

 then professor of mathematics ; and so great was his 

 progress, that, at the age of 15, he supported a mathe- 

 matical thesis, which he dedicated to the Duke of 

 Burgundy. In the year 1694, at the age of 17, he 

 was admitted into the Academy of Sciences ; and, 

 in the year 1695, he accompanied his father to Italy, 

 assisted him in verifying the meridian line at the 

 church of St Petronius, measured the length of the 

 Roman and Greek foot, and determined the latitude 

 of several of the cities through which he passed. 

 Upon his return from Italy he went to Holland, 

 where he determined the latitude of several places, 

 and discovered some errors which Snellius had com- 

 mitted in his measurement of the earth. Towards 

 the end of the year 1696, he undertook a journey to 

 England, where he became acquainted with Newton, 

 Halley, Flamstead, Gregory, and Wallis, and after 

 remaining some time, he returned to France with an 

 additional ardour for his favourite science, and adorn- 

 ed with the title of Fellow of the Royal Society. 



In the year 1712, James Cassini succeeded his fa- 

 ther as astronomer at the Royal Observatory of Pa- 

 ris ; and every volume of the Memoirs of the French 

 1 



