20 SCIENCE OF THE GREEKS. PT. 1. 



Aristarchus. There was, however, one Greek astrono- 

 mer named Aristarchus, who discovered the real movement 

 as we know it now. Aristarchus was born in Samos, some 

 time in the third century before Christ, but he came to Alex- 

 andria, and was tutor to the sons of one of the Ptolemies. 

 He taught that the sun was immovable like the fixed stars, 

 and that it was the earth which travelled round the ecliptic. 

 He knew also that our earth does not stand quite upright in 

 its journey round the sun, but that a line drawn through the 

 earth from the north to the south pole would be sloping or 

 oblique to the ecliptic, and that this obliquity is the cause of 

 our four seasons. 



If you do not understand this you can work it out with 

 your ball, using a lamp to represent the sun. First draw. an 

 ink-line round the middle of your ball for the equator, then 

 put your finger and thumb at the two ends of the ball to 

 represent the two poles. Do not hold the ball upright, but 

 bring your thumb nearer to you than your finger.. A line 

 drawn through the ball from your finger to your thumb will 

 now be inclined^ and will represent the inclined axis of the 

 earth. Now look at the light and shade on the ball : the 

 north pole, which is turned towards the lamp, will be in full 

 light, and will have the long days of summer ; the south 

 pole turned towards you will be in the dark, enduring its 

 long winter night. Pass the ball on to your right, and when 

 you have gone round a quarter of a circle the poles will 

 both have equal light, and the southern spring and northern 

 autumn have arrived. Pass on again, and at the next 

 quarter the south pole will be in summer and the north pole 

 in winter, while at the fourth and last point you have the 

 northern spring and the southern autumn. This was what 

 Aristarchus discovered, namely, that the changing seasons 

 are entirely caused by the earth having its axis (or the line 



