1\ E P 
protection tlie fyftem of Ptolemy with a 7 .eal with which 
the had before been feen to efpoufe the caul'e ot religion 
alone, but a hod: of other opponents arofe again ft them; 
for the idea of relinquithing the old opinion was (till too 
revolting; and attacks upon the new fyftem, yet deficient 
in the-means of defence, were the lefs difficult, as they 
feemed to be encouraged by the Scriptures themfelves. 
Kepler had been front his earlieft years a partifan of 
the Copernican fyftem, and fuch he continued at the time 
of his mod intimate connection with Tycho, though the 
latter was the author of a new fyftem, defigned to recon¬ 
cile Ptolemy’s with that of Copernicus. True as it is 
that the latter, attacked oti every fide, would have 
■been unable to maintain its ground without Kepler, 
and would at molt 'have flione a mere hiftorical datum ; 
Hill he never undertook its formal vindication ; blit the 
three celebrated laws which he difcovered, and which are 
known by his name, eftablilhed it on a bafis that is not to 
be lhaken. Kepler’s three laws are as follow : i. That 
the planets do not revolve in circular but in elliptical or¬ 
bits round the fun, which is their common centre, a. The 
times which a planet requires to perform part of its el¬ 
liptical revolution, bear the fame proportion to each other 
as the fpaces of the elliptical furface between the arc al¬ 
ready palled, and the fun as the focus. 3. The fquares 
of "the periodic times of the planets are always in the 
lame proportion as the cubes of their mean diltances from 
the fun, This laft he difcovered loine years later than 
the two others. 
Thoufands of times fince the difcovery of thefe three 
laws, the moft fplendid monuments of Kepler’s exalted 
and penetrating genius, have they been employed in af- 
tronomy, and as often have they produced the moft im¬ 
portant refults, and been fo completely verified, that 
without them the empire of aftrpnomy, the queen of the 
phyfical fciences, would never have acquired its prefent 
extent. Now Kepler’s laws prefuppofe the Copernican fyf¬ 
tem, and are founded upon it; if therefore they have been 
univerfially found to hold good, it mull be impolfibleto raife 
any doubts concerning that fyftem. With the other fyf- 
tems of the univerfe they are totally incompatible. We 
are therefore reduced to the neceflity of relinquilhing the 
fyftem on their account, or of abandoning them for the 
fake of the fyftem. 
Thus was the earth reduced, through Kepler’s inqui¬ 
ries, to the rank of a mere planet; and it was no longer 
difficult to explain in a fatisfaftory manner, a great num¬ 
ber of its phenomena which were before incomprehenfi- 
ble. The next queftion to be refolved was, by what power 
the planets were kept in the elliptical orbits in which they 
revolved round the fun ? This queftion alfo Kepler has 
anfwered with fagacity, and for the greatelt part with ac¬ 
curacy. The laws of motion had juft been difcovered and 
afcertained by the celebrated Galileo. From thefe it re- 
fulted, that gravity is common to all bodies upon the 
earth, as they have all a tendency to the earth’s centre, 
and follow this tendency unlefs retrained by fome exter¬ 
nal power. Galileo’s difcovery relative to the earth was 
firft applied by Kepler to the heavenly bodies. It is gra¬ 
vity, as he very juitly alTerted, that prevents the removal 
of the planets to a greater difiance from the fun than the 
laws of nature require; it is the attraction of the fun 
which produces in the planets that tendency to unite with 
him which we denominate gravity, as the gravity of bo¬ 
dies on the earth is occalioned by the attraction of the 
latter. The reafon why the planets do not remove to a 
greater diftarice from the fun is hence perfectly evident; 
and we have at the prefent day no ftronger reafon to give 
for it than Kepler’s, neither have we occafion for any. 
But whence comes it that the planets do not approach 
nearer to the fun than the law of nature decrees, and are 
not at length abforbed by that luminary? The folution 
of this queftion led Kepler into contradiction of himfelf, 
and errors into which he would not have fallen, had he 
been acquainted with the theory of the centrifugal force. 
Vox.. XI. No. 7.86, 
K E P 631 
which alone is the caufe of that phenomenon. He af- 
ftimed that the planets have twoXides, the one with gra¬ 
vity, the other without if. When the former, which lie 
terms the friendly fide of them is turned towards the fun, 
they are attracted by that luminary; but when the latter, 
or the hojfile fide as he calls it, is in the fame direction, 
they are repelled by the fun with the lame force as they 
were before attracted ; and this is the reafon why they 
always continue at the lame diltance from him. 
Kepler claimed the honour of the firft difcovery of the 
folar lpots. The truth is, that they were difcovered by 
feveral perlbns at the fame time with him ; but he had fo 
far the priority, that he firft obferved them without a te- 
lefcope, in the fun’s rays received into a darkened room. 
This was in May 1607. On this occafion he fell into an 
error, which he loon afterwards perceived, in taking thefe 
fpots for the planet Mercury palling over the fun. He 
took great pains to find out the horizontal parallax of the 
moon, which with Galileo he confidered to be inhabited. 
Copernicus and Tycho had before him bellowed attention 
upon this invelligation ; but the calculation’s ot thefe 
three altronomers are deficient in that fubtilty which is 
requifite for afcertaining with precilion the moon’s dis¬ 
tance from the earth, for which purpole her parallax is 
employed. Belides the above, he made a great number 
of oblervations which later altronomers have taken with 
advantage for the ground-work of their inquiries. 
Among thefe, we lliall merely notice his oblervations oh. 
the comet which appeared in 1618. Fie followed that 
meteor with anxious folicitude, and was of opinion that 
the part of his orbit lying between the earth and the 
fun might be considered as a right line. 
The greateft geniules of the age efteemed Kepler ; and 
with lome of them he was upon terms of f riend (hip. 
Gafiendi owed much to the ftudy of his works, and oil 
the phyfical part of his fyftem they had the moft ddcifive 
influence. Des Cartes alio was a great admirer of Kep¬ 
ler ; he himfelf acknowledges that in dioptrics he took 
him for his mailer; but his phyfical and mathematical 
writings lufficiently attell that Kepler’s fervices to him 
were not confined to the fcience of dioptrics, and that in 
other departments of human knowledge he had been 
guided by Kepler’s ideas which he more or lefs interwove 
with his own. But perhaps it is the higheft praife that 
can be bellowed on Kepler to affert, that our immortal 
Newton would not have made his aftonilhing difcoveries, 
had not the German aftronomer preceded and cleared the 
way for him. Human life is too Ihort for the application 
of difcovered truths to individual cafes; and chance, which 
caufed the one to be born at an earlier, the other at a 
later, period; which compelled the one to create, and per¬ 
mitted the other to avail himfelf of what had been thus 
created; ought not to decide our judgment. Far be it 
from 11s to detract in the flighted degree from the admi¬ 
ration paid to Newton ; but juftice demands the remark 
that our countryman raifed his fuperftruflure on the 
foundation laid by the German, and that Newton’s glory 
reflefls luftre upon Kepler. 
KEP'LERS, a village of United America, in Eerks 
county, Pennfylvania, on the north branch of Schuylkill 
river : twenty-one miles north-north-weft of Reading, and 
thirty-two weft of Bethlehem. 
KE'POUH-DAG'HI, a mountain of Afiatic Turkey, 
in the government of Sivas : fixty miles eall of Sivas. 
KEP'PEL (Auguftus), a celebrated Englilh admiral, 
the lecond fon of William earl of Albemarle, was born 
April 2, 1725. He entered the fea-fervice while he was 
young, accompanied commodore Anfon round the world, 
and, by the zeal which he manifefted in his profelfion, was 
raifed to the firft honours which it had to bellow. The 
moft important occurrence in his life took place in 1778, 
when he had the command of the channel-fleet, to which - 
he had been appointed at the perfonal and urgent felicita¬ 
tion of the king. The particulars of the a.ftion in which 
he was engaged, and the trials that eafued, have been al- 
8 L ready 
