CASSINI. 
but the minister Colbert prevailed on him 
to stay, and he was naturalized in 1673 ; 
tlie same year also in wliich he was mar- 
ried. 
The Royal Observatory of Paris had 
been finished some time, and Cassini was 
appointed to be the first inhabiter ; wliich 
he took possession of in September, 1671, 
when he set hiniself with fresh alacrity to 
attend the duties of his profession. In 
1672 he endeavoured to determine the pa- 
rallax of Mars and the Sun ; and in 1677 
he proved that the diurnal rotation of Jupi- 
ter round his axis was performed in 9 hours 
58 minutes, from the motion of a spot in 
one of his larger belts : also in 1 684 he dis- 
covered four satellites of Saturn, besides 
that which Huygens had found out. In 
1693 he published a new edition of his 
“ Tables of Jupiter’s Satellites,” corrected 
by later observations. In 1695 he took a 
journey to Bologna, to examine the meri- 
dian line which he had fixed there in 1655 ; 
and he showed, in the presence of eminent 
mathematicians, that it had not varied in 
the least during that 40 years. In 1700 he 
continued the meridian line through I’rance, 
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 useful discove- 
ries, which he published from time to time, 
he died September the 14th, 1712, at 87 
years of age ; and was succeeded by his son 
James Cassini. 
Cassini (James), a celebrated French 
astronomer, and member of the several 
Academies of Sciences of France, England, 
Prussia, and Bologna, was born at Paris 
February 18, 1677, being the younger son 
of John Dominic Cassini, above mentioned, 
whom he succeeded as astronomer 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 philosophy 
at the Mazarine college, where the cele- 
brated Varignon was then professor of ma- 
thematics ; from whose assistance young 
Cassini profited so well, that at 15 years of 
age he supported a mathematical thesis 
with great honour. At tlie age of 17 he 
was admitted a member of the Academy of 
Sciences ; and the same year he accompa- 
nied his father in his journey to Italy, where 
lie assisted him in the verification of the 
meridian at Bologna, and other measure- 
ments. 
In 1712 he succeeded his father as astro- 
nomer royal at the Observatory. In 1717 
he gave to the Academy his researches on 
the distance of the fixed stars, in which he 
showed that the whole annual orbit of near 
200 millions of miles diameter, is but as a 
point in comparison of that distance. The 
same year he communicated also his disco- 
veries concerning the iiiHination of the or- 
bits of the satellites in general, and espe- 
cially 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 wliich is commonly behind or hid 
from pur view. 
In 1732 an important question in astrono- 
my exercised the ingenuity of our author. 
His father had determined, by his observa- 
tions, tliat tlie planet Venus revolved about 
her axis in the space of 23 hours : and M. 
Bianchini had published a work in 1729, in 
which he settled the period of the same 
revolution at 24 days 8 hours. From 
an examination of Bianchini’s observations, 
which were upon the spots in Venus, he 
discovered that he had intermitted his ob- 
servations 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 
determined the nature and quantity of the 
acceleration of the motion of Jupiter, at 
half a second per year, aqd of that of tlie 
retardation of Saturn at two minutes per 
year ; that tliese quantities would go on in- 
creasing for 2,000 years, and then would 
decrease again. In 1740 he published his 
‘‘ Astronomical Tables,” and his “ Elements 
of Astronomy which were very extensive 
and accurate works. 
Altiiough 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 ex- 
ample, experiments on electricity, or the 
light produced by bodies by friction. Ex- 
periments on the recoil of fire arms ; re- 
searches on the rise of the mercury in the 
barometer at different heights above the le- 
vel of the sea ; reflections on the perfect- 
ing of burning-glasses, and other memoirs. 
After a long and laborious life, oiir au- 
thor, James Cassini, lost his life by a fall in 
April, 1756, in the 80th year of his age, and 
