C A S S I N I. 



COJ 







Academy cont.iim numerous proofs, both of his as- 



biduity as an observer, and as a physical astronomer. 

 In the year 170.">, he pu-M-nt'-d his paper on the me- 

 thod of determining the longitude of places, by the 

 eclipses of the iUed stars and planets by the moon. 

 His researches on the magnitude of the fixed stars, 

 and th.ir distance from the earth, appeared in 17.7; 

 and, in the same year, In- published his Theory of 

 the Motion of the Satellites of Saturn. In 1720, 

 he published his work, entitled, l)e la (iruiidciir i 1 

 tit' lit /'//<.( <{< hi Tt'irc. In his paper on the revo- 

 lution of Venus round her axis, which was printed in 

 the Memoirs of the Academy for 1732, he confirmed 

 the results of his father's observations, by pointing out 

 the mistakes committed by Bianchini ; and this de- 

 termination has been completely established by the 

 very recent observations of M. Schroetcr. His at- 

 tention was next turned to the curious subject of the 

 acceleration of the mean motion of Jupiter, and the 

 retardation of that of Saturn ; and he shewed that 

 the mean motion of Jupiter should be accelerated 

 half a second every year, while that of Saturn was 

 retarded two minutes in the same time ; and that 

 these quantities should increase for 2000 years, and 

 afterwards diminish. 



In the year 1710, Cassini published his Elemens 

 d' Astronomic, accompanied with astronomical tables 

 of the sun, moon, planets, stars, and satellites. The 

 Elements of Astronomy were composed at the re- 

 quest of the Duke of Burgundy, who was solicit- 

 ous to have in his own language an elementary trea- 

 tise on that science. The astronomical tables, which 

 were long reckoned the most accurate, were after- 

 wards reprinted by his son, but with many errors, 

 from which the original edition was free. 



Although the attention of Cassini was chiefly di- 

 rected to the study and practice of astronomy, yet 

 the other branches of physical knowledge occasion- 

 ally attracted his notice. Besides 172 memoirs on 

 astronomical subjects, which were printed by the A- 

 cademy of Sciences, he published eight upon the fol- 

 lowing subjects : 



1. Experiences sur le rccul des armes a feu. Mem. 

 .lead. 1 703. Hist. 98. 



2. Reflexions sur les regies de la condensation de 

 1'air. Id. 1705, p. 61. and p. 272. 



3. Observations sur la lumiere des corps frottees. 

 Id. 1707. Hist. 3. 



4-. Experiences sur les armes a feu differemment 

 chargees. Id. 1707. Hist. 3. 



5. De la necessite de bien centrer le verre objectif 

 d'une lunette. Id. 1710, p. 223. 



6. Experiences de 1'efFet du vent a 1'egard du 

 thermometre. Id. 1710, p. 54-4-. 



7. Reflexions sur les observations du barometre 

 ui out etc faite sur les montagnes du Puy-de-Dome, 

 u Mont-d'Or, et du Canigou. Id. 1740. Hist. 79. 



8. Methode de se servir des Miroirs concaves, de 

 metal ou de verre pour tenir les metaux en fusion, 

 &c. Id. 174-7, p. 25. 



Our author was employed, along with Maraldi 

 and De la Hire the Younger, in completing the 

 measurement of a degree of the meridian, which had 

 been begun by Picard, and continued by Dominique 

 Cassini ; and he finished this work in the year 1718. 

 The latitudes observed in several points, in an ex- 



d 



tent of more than six degrees, shewed an inequality 

 in tht-fcc degrees; and M. Cassini maintained, that d<r 

 the degrees of the same meridian diminished towards * 

 the poles, and consequently that the earth WAS a pro- 

 late spheroid. This result, so contrary to the New- 

 tonian tltr'iry f gravity, induced the French go- 

 vernment to measure a degree at the equator and 

 near the poles, the result of which overturned the 

 opinion of our author. 



In the year 17O4, Cassini had been appointed mas- 

 ter of accounts, and he discharged the duties of this 

 office with such activity and zeal, that, in 1710', he 

 was one of the small number of magistrates who 

 were chosen to compose the Chamber of Justice. 



While our author was ou the road to hi* country 

 house at Thury, he was unfortunately overturned, 

 and, having become instantly paralytic, he died of 

 his wound on the 15th April 175G. 



Cassini was la*-ge and well made, and had a very 

 interesting physiognomy. Distinguished by piety 

 and beneficence, he was one of those persons who ob- 

 tain that universal esteem to which they were justly 

 entitled. In 1710, Cassini married Mademoiselle Du- 

 charmoi, the daughter of the Countess of Sissonne, 

 by whom he had six children, one of whom died 

 when young. His two daughters were well married, 

 and his three sous rose to eminence in their respec- 

 tive professions, (o) 



CASSINI DE TIIURY, C.ESAR FRANCOIS, was 

 the second son of James Cassini, and was born at 

 Paris on the 17th June 1719. He received hii ear- 

 liest instructions in astronomy and geometry from 

 M. M. Maraldi and Camus; and when he was scarcely 

 ten years of age, he calculated the phases of the to- 

 tal eclipse of the sun, which happened in the year 

 1727. At the age of eighteen, he accompanied his 

 father in his two jourmes, for the purpose of draw- 

 ing a perpendicular to the meridian of the observa- 

 tory from Strasburg to Brest ; and, in the year 1735, 

 he was received into the academy as adjunct super- 

 numerary at the early age of twenty-one. 



A general chart of France having been about this 

 time meditated, it became necessary to traverse the 

 kingdom with several lines parallel to the meridian, 

 and to the perpendicular to the observatory. Cas- 

 sini was charged with this undertaking ; and, as the 

 measurements taken by his father and grandfather 

 were not exempt from errors, he undertook to dr^.v 

 anew the meridian of Paris, by means of a new series 

 of triangles, smaller in number, and more advanta- 

 geously arranged, than those which liad been for- 

 merly used. 



A full account of this survey was published by Cas- 

 sini in the Memoirs of the Academy for 17-11, under 

 the title of Mcridicnne de I'observatoire de Paris ve- 

 rijtti- dans loutc I' ct endue du royattme, pardc nouvclles 

 observations* SfC. avic des observations d'Histoire na- 

 tun-llcjuites dans les provinces iraversees par la Meri- 

 diennc. The series of triangles used on this occasion, 

 parsed along the sea coast to Bayonne, traversed the 

 frontiers of Spain to the Mediterranean, stretched as 

 far as Antibes, arid round by the eastern frontier of 

 France to Dunkirk. This map of triangles was ter- 

 minated by two columns, on which were marked the- 

 longitude, latitude, and distance from Paris, of all the 

 towns comprehended in the chain of triangles. 



