of Toledo improved the solar tables very much. Ulugh Begh, grandson of
the great Tamerlane the Tartar, built a fine observatory at Samarcand
in the fifteenth century, and made a great catalogue of stars, the
first since the time of Hipparchus.

At the close of the fifteenth century King Alphonso of Spain employed
computers to produce the Alphonsine Tables (1488 A.D.), Purbach
translated Ptolemy's book, and observations were carried out in
Germany by Muller, known as Regiomontanus, and Waltherus.

Nicolai Copernicus, a Sclav, was born in 1473 at Thorn, in Polish
Prussia. He studied at Cracow and in Italy. He was a priest, and
settled at Frauenberg. He did not undertake continuous observations,
but devoted himself to simplifying the planetary systems and devising
means for more accurately predicting the positions of the sun, moon,
and planets. He had no idea of framing a solar system on a dynamical
basis. His great object was to increase the accuracy of the
calculations and the tables. The results of his cogitations were
printed just before his death in an interesting book, _De
Revolutionibus Orbium Celestium_. It is only by careful reading of
this book that the true position of Copernicus can be realised. He
noticed that Nicetas and others had ascribed the apparent diurnal
rotation of the heavens to a real daily rotation of the earth about
its axis, in the opposite direction to the apparent motion of the
stars. Also in the writings of Martianus Capella he learnt that the
Egyptians had supposed Mercury and Venus to revolve round the sun, and
to be carried with him in his annual motion round the earth. He
noticed that the same supposition, if extended to Mars, Jupiter, and
Saturn, would explain easily why they, and especially Mars, seem so
much brighter in opposition. For Mars would then be a great deal