THE PLANETS. 431 



Jupiter 5-20277 



Saturn 9-53885 



Uranus 19-18239 



Neptune 30-03628 



The simple observation of rapidly diminishing periods of 

 revolution, from those of Saturn and Jupiter to Mars and 

 Venus, led, at a very early time, under the assumption that 

 the planets were attached to movable spheres, to conjectures 

 as to the distances of these spheres from each other. As 

 there are no traces of methodically- instituted observations 

 and measurements to be found among the Greeks before the 

 time of Aristarchus of Samos, and the establishment of the 

 Alexandrinian Museum, a great difference arose in the hypo- 

 theses as to the arrangement of the planets and their relative 

 distances; whether according to the most prevailing system, 

 with reference to their distances from the Earth as the fixed 

 centre ; or, as among the Pythagoreans, with reference to the 

 distances from the focus of the universe. The principal 

 subject on which there was a discrepancy of opinion was the 

 position of the Sun, that is, its relative situation in reference 

 to the inferior planets and the Moon. 19 The Pythagoreans, 

 who considered number to be the source of all knowledge, 

 the real essence of all existing things, applied their theory 

 of numbers, the all-blending doctrine of numerical relations, 

 to the geometrical consideration of the five regular bodies, 

 to the musical intervals of tone which determine accord, and 

 form different kinds of sounds, and even to the system 



w Bockh, de Platonico Syst. p. xxiv. and in Philolaos, 

 p. 100. The succession of the planets which, as we have 

 just seen (Note 14), gave rise to the naming of the week-days 

 after the planetary deities, that of Geminus, is distinctly called 

 the oldest by Ptolenneus. (Almag. xi. cap. i.) He blames 

 the motives from which " the moderns have placed Venus 

 and Mercury beyond the Sun/' 



