PHYSICAL CONTEMPLATION OF THE UNIVERSE. 109 



opment of our experimental sciences. The history of the con- 

 templation of the universe, as I interpret its limits, designates 

 not so much the frequently-recurring oscillations between truth 

 and error, as the principal epochs of the gradual approxima- 

 tion to more accurate views regarding terrestrial forces and 

 the planetary system. It shows us that the Pythagoreans, 

 according to the report of Philolaiis of Croton, taught the pro- 

 gressive movement of the non-rotating Earth, its revolution 

 round the focus of the world (the central fire, hestia), while 

 Plato and Aristotle imagined that the Earth neither rotated 

 nor advanced in space, but that, fixed to one central point, it 

 merely oscillated from side to side. Hicetas of Syracuse, who 

 must, at least, have preceded Theophrastus, Heraclides Ponti- 

 cus, and Ecphantus, all appear to have had a knowledge of the 

 rotation of the Earth on its axis ; but Aristarchus of Samos, 

 and more particularly Seleucus of Babylon, who lived one 

 hundred and fifty years after Alexander, first arrived at the 

 knowledge that the Earth not only rotated on its own axis, 

 but also moved round the Sun as the center of the whole plan- 

 etary system. And if, in the dark period of the Middle Ages, 

 Christian fanaticism, and the lingering influence of the Ptol- 

 emaic school, revived a belief in the immobility of the Earth, 

 and if, in the hypothesis of the Alexandrian, Cosmas Indico- 

 pleustes, the globe again assumed the form of the disk of 

 Thales, it must not be forgotten that a German cardinal, 

 Nicholas de Cuss, was the first who had the courage and the 

 independence of mind again to ascribe to our planet, almost 

 a hundred years before Copernicus, both rotation on its axis 

 and translation in space. After Copernicus, the doctrines of 

 Tycho Brahe gave a retrograde movement to science, although 

 this was only of short duration ; and when once a large mass 

 of accurate observations had been collected, to which Tycho 

 Brahe himself contributed largely, a correct view of the struc- 

 ture of the universe could not fail to be speedily established. 

 "VVe have already shown how a period of fluctuations between 

 truth and error is especially one of presentiments and fanciful 

 hypotheses regarding natural philosophy. 



After treating of the extended knowledge of nature as a si- 

 multaneous consequence of direct observations and ideal com- 

 binations, we have proceeded to the consideration of those his- 

 torical events which have materially extended the horizon of 

 the physical contemplation of the universe. To these belong 

 migrations of races, voyages of discovery, and military expe- 

 ditions. Events of this nature have been the means of ac- 



