i88o.] The Evolution of Scientific Knowledge. 419 
extreme simplicity and generality, and one, therefoic, which 
exemplifies an early stage in evolution. But ere long this 
simplicity gave way to incipient complexity. To account 
for the way in which the appearances of different nights 
succeed each other, the sun also was supposed to move 
round among the stars on the surface of the concave sphere ; 
and, if we are to believe Pliny, Anaximander was the first 
to point out that the circle in which the sun moves is oblique 
to the circles in which the stars move about the poles. 
Other irregularities were in process of time discovered, and 
the celestial mechanism by which they were explained grew 
proportionally in complexity. The wandering planets changed 
their course, moving now forwards and now backwards ; and 
to account for this motion each was supposed to be placed 
on the rim of an invisible wheel, which revolves on its centre 
while it moves around the sphere. Such a wheel was called 
an epicycle. Then it was discovered that the motions of the 
sun and moon also were irregular, so that they too were 
placed on the rims of imaginary epicycles ; while it was 
found that, for purposes of calculation, the same results 
were reached if— abandoning the epicycle— the sun were 
supposed to revolve in a circular orbit in which the earth 
does not occupy a central position, but is placed rather 
nearer to one side. Such an orbit was called an eccentric. 
Finally, as further anomalies and irregularities were disco- 
vered in the motions of the sun, moon, and planets, further 
extensions of the hypothesis of eccentrics . and epicycles 
were rendered necessary until the. master-mind of Hippar- 
chus formulated and organised this system, the essence o 
which consists in the resolution of the apparently regular 
motions of the heavenly bodies into an assemblage of cir- 
cular and uniform motions. . 
In those days, it must be remembered, circular motions 
were the only motions admissible ; the idea of such dis- 
order among divine and eternal things as that they should 
sometimes move quicker, and sometimes slower, and some- 
times stand still,” was considered impious, for no one, it 
was said, “ would tolerate such anomaly in the movements 
even of a man who was decent and orderly. And thus 
there sprang up that complex system which gave rise to the 
celebrated saying of Alphonso X., of Castille, that if God 
had consulted him at the creation, ? the universe should have 
been on a better and simpler plan.” 
That the history of early astronomic thought above 
sketched exhibits an advance from the vague to the definite, 
and from the simple to the complex, while it shows also an 
