planets,
and the entire heavens completed a daily revolution in twenty-four
hours. After the death of Ptolemy no worthy successor was found to
occupy his place, the study of astronomy began to decline among the
Greeks, and after a time it ceased to be cultivated by that people.

The Arabs next took up the study of astronomy, which they prosecuted
most assiduously for a period of four centuries. Their labours were,
however, confined chiefly to observational work, in which they
excelled; unlike their predecessors, they paid but little attention to
speculative theories--indeed, they regarded with such veneration the
opinions held by the Greeks, that they did not feel disposed to question
the accuracy of their doctrines. The most eminent astronomer among the
Arabs was ALBATEGNIUS (680 A.D.). He corrected the Greek observations,
and made several discoveries which testified to his abilities as an
observer. IBN YUNIS and ABUL WEFU were Arab astronomers who earned a
high reputation on account of the number and accuracy of their
observations. In Persia, a descendant of the famous Genghis Khan erected
an observatory, where astronomical observations were systematically
made. Omar, a Persian astronomer, suggested a reformation of the
calendar which, if it had been adopted, would have insured greater
accuracy than can be attained by the Gregorian style now in use. In
1433, Ulugh Beg, who resided at Samarcand, made many observations, and
constructed a star catalogue of greater exactness than was known to
exist prior to his time. The Arabs may be regarded as having been the
custodians of astronomy until the time of its revival in another quarter
of the Globe.

After the lapse of many centuries, astronomy was introduced into Western
Europe in 1220, and from that date to the present time its career has
been one of triumphant progress. In 1230, a translation of Ptolemy's
'Almagest' from Arabic into Latin was accomplished by order of the
German Emperor, Frederick II.; and in 1252 Alphonso X., King of Castile,
himself a zealous patron of astronomy, caused a new set of astronomical
tables to be constructed at his own expense, which, in honour of his
Majesty, were called the 'Alphonsine Tables.' Purbach and Regiomontanus,
two German astronomers of distinguished reputation, and Waltherus, a man
of considerable renown, made many important observations in the
fifteenth century.

The most eminent astronomer who lived during the latter part o