Encyclopaedia Britannica, or, a Dictionary of arts, sciences, and miscellaneous literature : enlarged and improved. Illustrated with nearly six hundred engravings > Volume 3, ASS-BOO

ASTRONOMY.
23.
Several il-
luftrious
perfons ap¬
ply to the
ftudy of a-
ftronomy.
24
©bferva-
tions of
Tycho
Brahe.
circles. The firft of thefe was divided into 90 equal
parts, the fecond into 89, the third into 88, and fo
on, as low as 46 ; and thus, as the index of the qua¬
drant would always fall upon one or other of the divi-
fions, or very near it, the minutes might be known
by computation. He publifhed many treatifes on ma¬
thematical fubje&s, particularly one which dete&ed
the errors of Orontius, who had imagined that he
could fquare the circle, double the cube, &c. by find¬
ing two mean proportionals betwixt two right lines.
Appian’s chief work was entitled The C<rfarean Ajlro-
nomij; and was publilhed at Ingolftadt in 1540, de¬
dicated to the emperor Charles V. and his brother
Ferdinand. In this he {bowed how to refolve aftrono-
mical problems by means of inftruments, without either
calculations or tables ; to obferve the places of the
Hars and planets by the aftrolabe *, and to foretel
eclipfes and defcribe the figures of them : the whole
iliuftrated by proper diagrams. In his fecond book
he defcribes the method of dividing an agronomical
quadrant, and of ufing it properly. His treatife con¬
cludes with the obfervation of five comets. Gemma
Frifius wrote a commentary on a work of Appian en¬
titled his Cofmography, with many obfervations of eclip¬
fes. He invented alfo the aftronomical ring, and fe-
veral other inftruments, which, though they could not
boaft of much exaftnefs fuperior to others, were yet of
confiderable utility in taking obfervations at fea ; and
he is alfo memorable for being the firft who propofed a
time-keeper for determining the longitude at fea.—
George Joachim Rheticus was a fcholar of Copernicus,
to attend whofe lectures he gave up his profefforfhip of
mathematics at Wittemberg. For the improvement of
aftronomical calculations, he began to conftru61 a table
of fines, tangents, and fecants, for every minute and
ten feconds of the quadrant. In this work he firft
{bowed the ufe of fecants in trigonometry, and greatly
enlarged the ufe of tangents, firft invented by Regio¬
montanus $ but he aftigned for the. radius a much larger
number of places than had been done before, for the
greater exa£lnefs of calculation. This great work he
did not live to accomplith ; but it was completed by his
difciple Valentine Otho, and publifhed at Heidelberg
in 1594.
During this century, the lift of aftronomers was dig¬
nified by fome very illuftrious names. About the year
1561, William IV. landgrave of Heffe Caftel, applied
himfelf to the ftudy of aftronomy. With the afliftance
of Rothman and Burgius, the former an aftronomer, the
latter an excellent mathematical inftrument-maker, he
erefted an obfervatory on the top of his palace at Caffel,
and furniftied it with fuch inftruments as were then in
ufe, made in the beft manner the artifts of that age
could execute. With thefe he made a great number of
obfervations, which were by Hevelius preferred to
tbofe of Tycho Brahe, and which were publiftied by
Snellius in 1618. From thefe obfervations he deter¬
mined the longitudes and latitudes of 400 ftars, which
he inferted in a catalogue where their places are redli-
fied to the beginning of the year 1593.
Tycho Brahe began his obfervations about the fame
time with the landgrave of Hefl’e, already mentioned.
He obfcrved the great conjundlion of Saturn and Ju¬
piter in 1363 ; and finding the inftruments he could
procure very inaccurate, he made a quadrant capable
VOL. III. Part I.
25
of (howing fingle minutes, and likewife a fextant four
cubits radius. In 15.71, he difcovered a new liar in
the chair of Cafliopeia ; which induced him, like Hip¬
parchus, to make a catalogue of the ftars. This con¬
tained the places of 777 ftars, redtified to the year 1600 j
but inftead of the moon, which was ufed by the ancients
to conned! the places of the iun and ftars, Tycho fub-
ftituted Venus, as having little or no parallax, and yet
being like the moon vifible both day and night. By
the recommendation of the landgrave of Hefle, he
obtained from the king of Denmark the ifland of Hu-
enna, oppofite to Copenhagen, where an obfervatory
was built. The firft ftone of this building, afterwards
called Uraniburg, was laid in the year 1576. It was Account of
of a fquare form, one fide of it being about 60 feet in Uramburg,
length ; and on the eaft and weft fides were two round i>ls 0l,ler*
towers of 32 feet diameter each. The inftrumentsVUtor'V'
were larger and more folid than had ever been feen be¬
fore by any altronomer. They confifted of quadrants,
fextants, circles, femicircles, armillaeboth equatorial and
zodiacal, paralladlic rulers, rings, aftrolabes, globes,
clocks, and fun-dials. Thefe inftruments were fo di¬
vided as to {how fingle minutes j and in fome the arch
might be read off to 10 feconds. Moft of the divifions
were diagonal: but he had one quadrant divided ac¬
cording to the method invented by Nonius; that is, by
47 concentric circles. The whole expence is faid to
have amounted to 200,000 crowns. The method of
dividing by diagonals, which Tycho greatly admired,
was the invention of Mr Richard Chanceler, an Eng-
lifhman : Tycho, however, {hows, that it is not accu¬
rately true when ftraight lines are employed, and the
circles at equal diftances from each other 5 but that it
may be corre61ed by making circular diagonals, which
if continued would pafs through tire centre.
Tycho employed his time at Uraniburg to the beft
advantage ; but falling into difcredit on the death of
the king, he was obliged to remove to Holftein, and at
laft found means to get himfelf introduced to the em¬
peror, with whom he continued to his death. He is
well known to have been the inventor of a fyftem
of aftronomy, which bears his name ; and which he
vainly endeavoured to eftablilh on the ruins of that
of Copernicus : but the fimplicity and evident confo-
nancy to the phenomena of nature, difplayed in all
parts of the Copernican fyftem, foon got the better of
the unnatural and complicated fyftem of Tycho. His
works, however, which are very numerous, difcover him
to have been a man of vaft abilities. After his death
the caftle of Uraniburg quickly fell to decay, and in¬
deed feems to have been purpofely pulled down j for,
in 1652, when Mr Huet went to Sw'eden, it rvas almoft
level with the ground, and few traces of the walls could
be difcerned. None of the neighbouring inhabitants
had ever heard of the name of Tycho or Uraniburg,
excepting one old man, whom Mr Huet found out
with great difficulty, and who had been a fervant in
the family ! All the difcoveries of Purback, Regiomon¬
tanus, and Tycho, were collefled and publiflied in the
year 1621, by Longomontanus, who had been Tycho’s
favourite fcholar.
While Tycho refided at Prague with the emperor, Bifcoverles
he invited thither John Kepler, afterwards fo famousKepler,
for his difcoveries. Under the tuition of fo great
an aftronomer, the latter quickly made an amazing
C progrefs.