8' 7 6 CAS 
Royal Obfervatory of Paris bad been finiflied fome time 
before. The foundation of this noble pile was laid in 
1667, and the building completed in 1670. Of this obfer¬ 
vatory, Caftini was appointed to be the firft inhabiter ; 
which he took poffeflion of in Sept. 1671, when he let 
Iiimfelf with frefh alacrity to attend the duties of his pro- 
feffi&n. In 1672 he endeavoured to determine the parallax 
of Mars and the fun ; and in 1677 he proved that the diur¬ 
nal rotation of Jupier round his axis was performed in nine 
hours and fifty-eight minutes, from the motion of a fpot in 
one of his larger belts : alfo in 1684. he difcovered four 
fatellitesof Saturn, belides that which Huygens had found 
out. In 1693 he publiflied a new edition of his Tables of 
Jupiter’s Satellites, correfled by later obfervations. In 
2693 he took a journey to Bologna, to examine the meri¬ 
dian line, which he had fixed th.e're in 1655 ; and he (hew¬ 
ed, in the prefence of eminent mathematicians, that it had 
■not varied in the leaf! during thole forty years. In 1700 
he continued the meridian line through France, which Pi¬ 
card had begun, to the very l'onthern limits of that coun¬ 
try. After prefiding at the royal obfervatory for more 
than forty years, and making many excellent and ufeful 
dileoveries, which he publiflied from time to time, he died 
Sept. 14, 1712, at eighty-feven years of age, and was fuc- 
ceeded by his only Ion, James CalTini. His publications 
were very numerous; many of which appeared in the- 
early part of the Memoirs of the Royal Academy of 
France. 
CASSl'NI (James), a celebrated French aftronomer, 
and member of the feveral academies of fciences of Eng¬ 
land, France, Prufiia, and Bologna, was born at Paris, F'eb. 
18, 1677, being the younger fon of John Dominic -CalTini, 
above mentioned, whom lie fucceeded as aftronomer at the 
royal obfervatory, the elder fon having loft his-1 ife at the 
battle of La Hogue. After his firft tuition in his father’s 
houfe, he was lent to ftudy philofophy at the Mazarine 
college, where the celebrated Varignnn was then profef- 
for of mathematics; from whole aftiftance young Caffini 
profited fo well, that at fifteen years of age, he fupported 
a mathematical tliefis with great honour. At the age of 
17, he was admitted a member of the academy of fciences, 
and the fame year he accompanied his father in his jour¬ 
ney to Italy, where he allifted him in the verification of 
the meridian at Bologna, and other meafurements. On 
his return lie made other fimilar operations in a journey 
into Holland, where he difcovered fome errors in the mca- 
fure of the earth by Snell, the refult of which was com¬ 
municated to the academy in 1702. He made alfo a vilit 
to England in 1696, where he was made a member of the 
Royal Society. In 1712 he fucceeded his father as aftro¬ 
nomer royal at the obfervatory. In 1717 he gave to the 
Academy his refearch.es on the di(lance of the fixed ftars, 
in which he fliewed that the whole annual orbit, of near 
two hundred millions of miles diameter, is but as a point 
in comparifon of that diftance. The fame year he com¬ 
municated his difeoveries concerning the inclination of the 
orbits of the fatellites in general, and efpecially of thofe 
of Saturn’s fatellites and ring. I11 1725 he undertook to 
determine the caufe of the moon’s libration,by which (lie 
fliews fometimes a little towards one fide, and fometimes 
a little on the other, of that half which is commonly be¬ 
hind, or hid from our view. I11 1732 an important quef- 
tion in aftronomy exercifed the ingenuity of our author. 
His father had determined, by his obfervations, that the 
planet Venus revolved about her axis in the lpace of 
twenty-three hours; and M. Bianchini had publiflied a 
work in 1729, in which he fettled the period of the fame 
revolution at twenty-four days eight hours. From an 
examination of Bianchini’s obfervations, which were upon 
the (pots in Venus, he difcovered that he had intermitted 
his obfervations for the (pace of tiiree hours, from which 
caufe he had probably miftaken new fpots for the old 
ones, and fo had been led into the miftake. He Toon after 
determined tlie nature and quantity of the acceleration of 
the motion of Jupiter at half a feconti per year, and of that 
CAS 
of the retardation of Saturn at two miiVUtesper year j that 
the fe quantities would go on increafing for 2000 years, 
and then would deereafe again. In 1740 lie pnblillied his 
Aftronomical Tables, and his Elements of Aftronomy, 
very extenfive and accurate works. But although aftro¬ 
nomy was the principal object of his confideration, he did 
not confine himfelf abfoluteiy to that branch, but made 
occaficnal excurfions into other fields. We owe to him 
Experiments on Eleiftriciry, or the light produced by fric¬ 
tion ; Experiments on the Recoil of Fire-arms; Re- 
(earches on the Rife of the Mercury in the Barometer, at 
different Heights above the Level of the Sea; ReHebiions 
on the Perfecting of Burning-glades; and other memoirs. 
The French Academy had properly judged, thet one of 
its moft important objects was the meafurement of the 
earth- I11 1669 Picard meafured a little more than a de¬ 
gree of latitude to the north of Paris; bur, as that ex¬ 
tent appeared tooTmall from which to conclude the whole- 
circumference with lufficient accuracy, it was refolved to 
continue that meafurement on the meridian of Paris to 
the north and Couth, through the whole extent of the 
country. Accordingly, in 1683, the late M. de la Hite 
continued that on the north lide of Paris, and the older 
CaHini that on the Couth (ide. The latter was aftifted in 
1700 in the continuation of this operation, by his Ion. The 
fame work was farther continued by the fame academi¬ 
cians; and finally, the part left unfinifhed by de la Hire 
in the north, was finiflied, in 1718, by James Caflini, with 
the late Maraldi, and de la Hire the younger. After a 
long and laborious life, lie died by a fall, in April, 1756, 
in the eightieth year of his age, and was fucceeded in tlie 
Academy and Obfervatory by his fecond fon, Cefar Fran¬ 
cois de Tliury. He publiflied a Treatife on the Magni¬ 
tude and Figure of the Earth ; alfo, the Elements or The¬ 
ory of the Planets, with Tables; befides an infinite num¬ 
ber of papers in the Memoirs of the academy, from the 
year 1699 to 1755. 
CASSl'NI DE THURY (Cefar Francois), a celebrated 
French aftronomer, direbtorof the obfervatory, petitioner 
aftronomer, and member of moft of the learned focieties of 
Europe, was born at Paris, June 17, 1714, being the fe¬ 
cond (on of James Caftini, whofe talents lie inherited and 
fupported with great honour. He received his firft lef- 
fons in aftronomy and mathematics from MM. Maraldi 
and Camus. He was hardly ten years of age when he cal¬ 
culated the phafes of the total eclipfe of the fun of 1727, 
At the age of eighteen he accompanied his father in his two 
journies undertaken for drawing the perpendicular to the 
obfervatory meridian from Strafbourg to Breft. From 
that time a general chart of France was devifed; for 
which purpofe it was neceflary to traverfe tlie country 
by feveral lines parallel and perpendicular to the meridian 
of Paris, and Caftini was charged with the conduct of this 
bufinefs. He did not content himfelf with the meafure of 
a degree by Picard: fu(peeling even that the meafures 
which had been taken by his father and grandfather were 
not exempt from fome errors, which the imperfeitions of 
their inftruments, at lead, would be liable to, he again 
undertook to meafure the meridian of Paris, by means of 
a new feries of triangles, of a fmaller number, and more 
advantageoufly difpofed. This great work was publiflied 
in 1740, with a chart, (hewing the new meridian of Paris, 
by two different feries of triangles, pafling along the fea- 
coafts, to Bayonne, traverfing the frontiers of Spain, to 
the Mediterranean and Antibes, and thence along the eaf- 
tern limits of France to Dunkirk, with parallel and per- 
dendicular lines deferibed at the diftance of 6000 toifes 
fiom one another, from (ide to (ide of the country. A 
tour which he made in Flanders, in company with the 
king, about 1741, gave rife to the particular chart of 
France at the inftanceof the king. Caftini publiflied dif¬ 
ferent works relative to tliefe charts, and a great number 
of the (beets of the charts themfelves. 
In 1 7 !j 1 Caffini undertook an expedition into Germany, 
for the purpofe of continuing to Vienna the perpendicular 
of 
