KEPLER

In order to emphasise the importance of the reforms introduced into

astronomy by Kepler, it will be well to sketch briefly the history of

the theories which he had to overthrow. In very early times it must

have been realised that the sun and moon were continually

changing their places among the stars. The day, the month, and the

year were obvious divisions of time, and longer periods were

suggested by the tabulation of eclipses. We can imagine the respect

accorded to the Chaldaean sages who first discovered that eclipses

could be predicted, and how the philosophers of Mesopotamia must

have sought eagerly for evidence of fresh periodic laws. Certain of

the stars, which appeared to wander, and were hence called planets,

provided an extended field for these speculations. Among the

Chaldaeans and Babylonians the knowledge gradually acquired was

probably confined to the priests and utilised mainly for astrological

prediction or the fixing of religious observances.