42 6 ASTRONOMY. 
be made of the next tranfif of Venus in determining the 
diftaace of the Sun from the Earth. He compofed ta¬ 
bles of the Sun, Moon, and all the planets, which are ftill 
in great repute ; with which he compared the obfervations 
he made of the Moon at Greenwich, amounting to near 
1500, and noted the differences. He recommended tire 
method of determining the' longitude by the Moon’s dif- 
tances from the Sun and certain fixed ftars; a method 
which had before been noticed, and which has fince been 
carried into execution, more particularly at the infiance of 
Dr. Mafkelyne, the prefent aflronomer-royal. 
On the death of Dr. Halley, in 1742, he was fucceeded 
by Dr. Bradley, as afironomer-royal at Greenwich. The 
accuracy of his obfervations enabled him to deteft the 
fmaller inequalities in the motions of the planets and fixed 
fiars. The confequence of this accuracy was, the difco- 
very of the aberration of light, the nutation of the Earth’s 
axis, and a much greater degree of perfection in the lunar 
tables. He obferved the places, and computed the ele¬ 
ments, of the comets, which appeared in the years 1723, 
1736, 1743, and 1737; made new and accurate tables of 
of the motions of Jupiter’s fatellites ; and, from a multi¬ 
tude of obfervations of the luminaries, conftrufted the 
mofi accurate table of refraftions yet extant. Alfo, with 
a very large tranfit inftrument, and a new mural quadrant 
of eight feet radius, conftrudted by Mr. Bird, in 1750, he 
made an immenfe number of obfervations for fettling the 
places of all the fiars in the Britifh catalogue, together 
with near 1500 places of the Moon, the greater part of 
which he compared with Mayer’s tables. 
In the mean time aftronomers elfewhere were affiduous 
in their endeavours to promote this fcience. The theory 
of the Moon was particularly confidered by Clairault, d'A¬ 
lembert, Euler, Mayer, Simplon, and Walmefley; but 
efpecially by Clairault, Euler, and Mayer, who computed 
complete fets of lunar tables : thofe of the laft of thefe 
authors, for their fuperior accuracy, were rewarded with 
a premium of 3000I. and brought into ufe in the compu¬ 
tation of the Nautical Ephemeris, publifited by the Board 
of Longitude. The mofi: accurate tables of the fatellites 
of Jupiter were compofed, from obfervations, by Wargen. 
tin, an excollent Swedifti aftronomer. Among the many 
French afironomers who contributed to the advancement 
of the fcience, it was particularly indebted to De la Caille, 
for an excellent fet of folar tables; who, in 1750, went to 
the Cape of Good Hope to make obfervations in concert 
with the mofi celebrated aftronomers in Europe, for de¬ 
termining the parallax of Mars and the Moon, and thence 
that of the Sun, which it was concluded did not much 
exceed 10". Here he re-examined and adjufted, with great 
accuracy, the fiars about the fouthern pole, and alfo mea- 
fured a,degree of the meridian. In Italy the fcience was 
afltduoufly cultivated by Bianchini, Bofcovich, Frill, Man- 
fredi, Zanotti, and many others ; in Sweden by Wargen- 
tin already mentioned, Blingenftern, Mallet, and Planman ; 
and in Germany by Euler, Mayer, Lambert, Grifchow, 
and others. 
Dr. Bradley died in 1762, and was fucceeded in his of¬ 
fice of afironomer-royal by Mr. Blifs, Savilian profefibr 
of afironomy ; who, being in a declining ftate of health, 
did not long enjoy it. In 1765, he was fucceeded by Dr. 
Nevil Maikelyne, the prefent afironomer-royal, who, in 
January 1761, was lent by the Royal Society, at a very 
early age, to the ifiand of St. Helena, to obferve the tran¬ 
fit of Venus over the Sun, and the parallax of the liar Si¬ 
rius. The firft of thefe objects partly failed, by clouds 
preventing the fight of the fecond internal contact; and 
the fecond alfo, owing to Mr. Short having fufpended the 
plumb-line by a loop from the neck of the central pin. 
However, our aftronomer indemnified himfelf by many 
other valuable obfervations : thus, he obferved at St. He¬ 
lena, the tides ; the horary parallaxes of the Moon ; and 
the going of a clock, to find, by companion with its pre¬ 
vious going which had been obferved in England, the dif¬ 
ference of gravity at the two places: alfo, in going out 
and returning, he praftifed the method of finding the Ion. 
gitude by the lunar d;fta'nces taken with Hadley’s quadrant, 
making out rules for the ufe of fearnen, and teaching the 
method to the officers on-board the fhip; which was ex¬ 
plained in the Phil. Tranf. for 1762, and more fully after, 
wards in the Britifli Mariner’s Guide, publilhed in the 
year 1763. In September, 1763, he failed for the ifiand 
of Barbadoes, to fettle the longitude of the place, to exa¬ 
mine Harrifon’s time-piece, and to try Irwin’s marine- 
chair. While at Barbadoes, he made many other obfe<* 
vations, and amongft them many relating to the Moon’s ho¬ 
rary parallaxes. Returning to England in the latter part 
of the year 1764, lie was appointed in 1763 to fucceed Ma\ 
Blifs as afironomer-royal; and he immediately recommend¬ 
ed to the Board of Longitude the lunar method of finding 
the longitude, and propofed to it the project of a Nautical 
Almanac, to be calculated and publifiied to facilitate that 
method ; this being agreed to, the firft volume was pub- 
Jiflied for 1767, and has continued ever fince under his di. 
redtion, to the great benefit of navigation. 
Finally, the difeoveries and improvements of Dr. E 5 erf- 
chel, by the invention of his powerful telefcopes, form a 
new era both in fpeculative and practical aftronomy. His 
improved catalogue of the fixed ftars will alfo be found 
of infinite utility to future obfervers. Indeed, the early 
care of practical aftronomers feems very wifely to have 
been that of numbering the fixed ftars and of reducing 
them to a regular catalogue, in order that pofterity might 
know whether any changes had been difeovered in the ftar- 
ry firmament of the heavens. Hipparchus of Rhodes, 
about 120 years before Chrift, is generally allowed to have 
been the firft who attempted a compilation of this kind. 
Ptolemy however mentions, that Tymocharius and Arif- 
tyllus left feveral obfervations made 180 years before. The 
catalogue of Hipparchus contained 1022 ftars, with their 
latitudes and longitudes, which Ptolemy publifiied, with 
the addition of four more. Thefe aftronomers made their 
obfervations with an armillary fphere, as before obferved ; 
placing the armilla, or hoop reprefenting the ecliptic, to 
coincide with the ecliptic in the heavens by means of the 
Sun in the day-time, and then they determined the place 
of the Moon in refpedt to the Sun by a moveable circle 
of latitude. The next night, by the help of the Moon 
(whofe place before found they corrected by allowing for 
its motion in the interval of time), they placed the hoop 
in fuch a fituation as was agreeable to the prefent moment 
of time, and then compared, in like manner, the places of 
the ftars with the Moon. Thus they found the latitudes 
and longitudes of the ftars; it could not, however, be 
done with fuch an inftrument to any very great degree of 
accuracy. Ptolemy adapted his catalogue to the year 137 
after the Chriftian era; but fuppofing, with Hipparchus 
who made the difeovery, the precefiion of the equinoxes 
to be one degree in 100 years, inftead of about feventy- 
two years, lie only added 2 0 40' to the numbers in Hippar¬ 
chus for 265 years (the difference of the epochs), inftead 
of 3 0 42' 22", according to Dr. Malkelyne’s Tables. To 
compare his tables, therefore, with the prefent, we mult 
firft increafe his numbers by i° 2' 22", and then allow for 
the precefiion from that time to this. The next aftrono¬ 
mer who numbered the fixed ftars anew, was Ulugh Beigh, 
the grandfon of Tamerlane the Great; he made a catalogue 
of 1022 ftars, reduced to the year 1437. William, the 
moft illuftrious landgrave of Heffe Caffel, made a cata¬ 
logue of 400 ftars which he obferved ; he computed their 
latitudes and longitudes from their obferved right afeen- 
fions and declinations. In the year 1610, Tycho Brahe’s 
catalogue of 777 ftars was publifiied from his own obfer¬ 
vations, made with great care and diligence. It was af¬ 
terwards, in 1627, copied into the Rodolphine Tables, and 
increafed by 223 ftars from other obfervations of Tycho. 
In.ftead of a zodiacal armilla, Tycho fubftituted the equa¬ 
torial armilla, by which he obferved the difference of right 
afcenlions, and the declinations, out of the meridian, the 
meridian altitude being always made ufe of to confirm the 
ethers 0 
