74 A SHORT HISTORY OF SCIENCE 



the ligatures of heaven extended; for this light was the band of 

 heaven, like the hawsers of triremes, keeping the whole circumference 

 of the universe together. 



Aristotle sums up Plato's theories not too clearly in the 

 words : 



In a similar manner the Tim&us shows how the soul moves the 

 body because it is interwoven with it. For consisting of the elements 

 and divided according to the harmonic numbers, in order that it 

 might have an innate perception of harmony and that the universe 

 might move in corresponding movements, He bent its straight line 

 into a circle, and having by division made two doubly joined circles 

 out of the one circle, He again divided one of them into seven circles 

 in such a manner that the motions of the heavens are the motions of 

 the soul. 



Plato probably had no real knowledge of those deviations of 

 the planets from uniform circular motion, which were to engross 

 the attention of succeeding philosophers and astronomers. His 

 system is consistently geocentric, and assumes a stationary 

 earth. According to Plutarch: 



Theophrastus states that Plato, when he was old, repented of 

 having given the earth the central place in the universe which did 

 not belong to it, 



this presumably indicating an inclination towards the theories 

 of the later Pythagoreans. 



Plato adopts the Pythagorean or Empedoclean hypothesis of 

 the four elements, the component particles being assumed to have 

 respectively the shapes of the cube (earth), icosahedron (water), 

 octahedron (air), and tetrahedron (fire). 



All the heavenly bodies are looked on as divine beings, the first of 

 all living creatures, the perfection of whose minds is reflected in their 

 orderly motions. 



Summing up an extended discussion of Plato's astronomical 

 theories, Dreyer says : 



