SCIENCE IN THE ANCIENT WORLD 41 



as the centre, Hipparchus showed that the apparent 

 motion of the sun could be explained by supposing 

 that it was carried round a central point in an orbit or 

 epicycle, while this orbit, sun and all, was carried round 

 the earth in an immensely larger circular orbit or 

 cycle. From direct observation, solar tables could 

 then be calculated, from which the sun's position at 

 any future time could be predicted, and even solar 

 and lunar eclipses foretold with some accuracy. These 

 ideas were extended with success to the moon also, 

 Babylonian records being pressed into service for the 

 dates of past eclipses. 



According to the accepted view, continued motion 

 needed a continued moving force, and thus it was 

 necessary to suppose the skies filled with crystal 

 circles, which, cycles and epicycles, carried round the 

 heavenly bodies as they revolved. 



It is easy to ridicule this scheme of astronomy in 

 the light of modern times ; yet the fact remains 

 that, false as the theory was, it served successfully 

 to interpret knowledge for many centuries, and 

 guided the labours of such a competent astronomer as 

 Ptolemy. The theory most fruitful at a given time 

 is not always that which eventually survives, but 

 may be too much in advance of the age to be usefully 

 employed. 



If astronomical phenomena are the more striking, 



and therefore the first to arrest attention, the problem 



The Problem * tne nature of matter cries equally for 



of Matter. an explanation to thoughtful minds, 



And so we find the Ionian philosophers tracing the 



changes of substance from earth and water to the 



