CAS 



CAS 



dian line through France, which Picard 

 had begun, to the very southern limits of 

 that country. 



After our author had resided at the 

 Royal Observatory for more than 40 

 years, making many excellent and use- 

 ful discoveries, which he published from 

 time to time, he died September the 14th, 

 1712, at 87 years of age ; and was suc- 

 ceeded by his son James Cassini. 



CASSINI (JAMES.) a celebrated French 

 astronomer, and member of the several 

 Academies of Sciences of France, Eng- 

 land, Prussia, and Bologna, was born at 

 Paris, Feburary 18,1677, beingthe young- 

 er son of John Dominic Cassini, above 

 mentioned, whom he succeeded as as- 

 tronomer at the Royal Observatory, the 

 elder son having lost his life at the battle 

 of La Hogue. 



After his first studies in his father's 

 house, in which it is not to be supposed 

 that mathematics and astronomy were 

 neglected, he was sent to study philoso- 

 phy at the Mazarine college, where the 

 celebrated Varignon was then professor 

 of mathematics ; from whose assistance 

 young Cassini profited so well, that at 15 

 years of age he supported a mathemati- 

 cal thesis with great honour. At the age 

 of 17 he was admitted a member of the 

 Academy of Sciences ; and the same year 

 he accompanied his father in his journey 

 to Italy, where he assisted him in the 

 verification of the meridian at Bologna, 

 and other measurements. 



In 1712 he succeeded his father as as- 

 tronomer royal at the Observatory. In 

 1717 he gave to the academy his re- 

 searches on the distance of the fixed stars, 

 in which he showed that the whole annu- 

 lar orbit of near 200 millions of miles dia- 

 meter is but as a point in comparison of 

 that distance. The same year he com- 

 municated also his discoveries concerning 

 the inclination of the orbits of the satel- 

 lites in general, and especially of those of 

 Saturn's satellites and ring. In 1725 he 

 undertook to determine the cause of the 

 moon's libration, by which she shows 

 sometimes a little towards one side, and 

 sometimes a little on the other, of that 

 half which is commonly behind or hid 

 from our view. 



In 1732 an important question in astro- 

 nomy exercised the ingenuity of our au- 

 thor. His father had determined, by his 

 observations, that the planet Venus re- 

 volved about her axis in the space of 

 23 hours : and M. Bianchini had publish- 

 ed a work in 1729, in which he settled 

 the period of the same revolution at 24 



days 8 hours. From an examination ot 

 Bianchini's observations, which were up- 

 on the spots in Venus, he discovered that 

 he had intermitted his observations for 

 the space of three hours, from which 

 cause he had probably mistaken new spots 

 for the old ones, and so had been led into 

 the mistake. He soon afterwards deter- 

 mined the nature and quantity of the ac- 

 celeration of the motion of Jupiter at 

 half a second per year, and of that of the 

 retardation of Saturn at two minutes per 

 year ; that these quantities would go on 

 increasing for 2000 years, and then would 

 decrease again. In 1740 he published his 

 " Astronomical Tables," and his " Ele- 

 ments of Astronomy;" which were very 

 extensive and accurate works. 



Although astronomy was the principal 

 object of our author's consideration, he 

 did not confine himself absolutely to that 

 branch, but made occasional excursions 

 into other fields. We owe also to him, for 

 example, experiments on electricity, or 

 the light produced by bodies by friction; 

 experiments on the recoil of fire-arms ; 

 researches on the rise of the mercury in 

 the barometer at different heights above 

 the level of the sea; reflections on the 

 perfecting of burning-glasses, and other 

 memoirs. 



After a long and laborious life our au- 

 thor, Jarnes Cassini, lost his life by a fall, 

 in April 1756, in the 80th year of his age, 

 and was succeeded in the Academy and 

 Observatory by his second son, Caesar 

 Franc. ois de Thury ; who also distinguish- 

 ed himself in the sciences connected with 

 astronomy ; and, as well as his father and 

 grandfather, published many valuable 

 works. He died in 1784, of the small 

 pox, and was succeeded by his only son 

 count John Dominic Cassini. 



CASSIOPEIA, in astronomy, a con- 

 stellation of the northern hemisphere, si- 

 tuated opposite to the Great Bear, on the 

 other side of the pole. See ASTRONOMY. 



In the year 1572, a remarkable new star 

 appeared in this constellation, surpassing 

 Sirius or Lyra in brightness and magni- 

 tude. It appeared even bigger than Ju- 

 piter, which, at that time, was near his 

 perigee, and by some was thought equal 

 to Venus, when she is in her greatest lus- 

 tre; but in a month it began to diminish 

 in lustre, and in about eighteen months 

 entirely disappeared. 



It alarmed all the astronomers of that 

 age, many of whom wrote dissertations 

 on it ; among the rest, Tycho Brahe, Kep- 

 ler, Maurolycus, Lycetus, Gramineus, 

 &c. Beza, the Landgrave of Hesse, Rosa, 



