tributed to the earth itself
instead of having a separate annual epicycle for each planet and for the
sun. Of the seventy odd circles or epicycles required by the latest form
of the Ptolemaic system, Copernicus succeeded in dispensing with rather
more than half, but he still required thirty-four, which was the exact
number assumed before the time of Aristotle. His considerations were
almost entirely mathematical, his only invasion into physics being in
defence of the "moving earth" against the stock objection that if the
earth moved, loose objects would fly off, and towers fall. He did not
break sufficiently away from the old tradition of uniform circular
motion. Ptolemy's efforts at exactness were baulked, as we have seen, by
the supposed necessity of all the orbit planes passing through the
earth, and if Copernicus had simply transferred this responsibility to
the sun he would have done better. But he would not sacrifice the old
fetish, and so, the orbit of the earth being clearly not circular with
respect to the sun, he made all his planetary planes pass through the
centre of the earth's orbit, instead of through the sun, thus
handicapping himself in the same way though not in the same degree as
Ptolemy. His thirty-four circles or epicycles comprised four for the
earth, three for the moon, seven for Mercury (on account of his highly
eccentric orbit) and five each for the other planets.

It is rather an exaggeration to call the present accepted system the
Copernican system, as it is really due to Kepler, half a century after
the death of Copernicus, but much credit is due to the latter for his
successful attempt to provide a real alternative for the Ptolemaic
system, instead of tinkering with it. The old geocentric system once
shaken, the way was gradually smoothed for the heliocentric system,
which Copernicus, still hampered by tradition, did not quite reach. He
was hardly a practical astronomer in the observational sense. His first
recorded observation, of an occultation of Aldebaran, was made in 1497,
and he is not known to have made as many as fifty astronomical
observations, while, of the few he did make and use, at least one was
more than half a degree in error, which would have been intolerable to
such an observer as Hipparchus. Copernicus in fact seems to have
considered accurate observations unattainable with the instruments at
hand. He refused to give any opinion on the projected reform of the
calendar, on t