106 HISTORY OF THE PHYSICAL 



back a belief in the immobility of the earth, and if, in the 

 view of the Alexandrian Cosmas Indicopleustes, its form even 

 became again that of the disk of Thales, on the other hand it 

 should be remembered that a German Cardinal, Nicolaus de 

 Cuss, almost a century before Copernicus, had the mental free- 

 dom and the courage to reascribe to our planet both a rotation 

 round its axis, and a progressive movement round the sun. 

 After Copernicus, TychoBrahe's doctrine wasastepbackwards; 

 but the retrogression was of short duration. When once a 

 considerable mass of exact observations had been assembled, 

 to which Tycho himself largely, contributed, the true view of 

 the structure of the universe could not be long repressed. 

 We have here shewn how the period of fluctuations is espe- 

 cially one of presentiment and speculation. 



Next to the " enlarged knowledge of nature," resulting at 

 once from observation and from ideal combinations, I have 

 proposed tonotice "great events," by which the horizon of the 

 contemplation of the universe has been extended. To this class 

 belong the migration of nations, remarkable voyages, and mili- 

 tary expeditions ; these have been instrumental in making 

 known the natural features of the earth's surface, such as 

 the form of continents, the direction of mountain chains, 

 the relative elevation of high plateaus, and sometimes 

 oy the wide range over which they extended, have even 

 provided materials for the establishment of general laws of 

 nature, in these historical considerations, it will not be 

 necessary to present a connected tissue of events ; it will be 

 sufficient to notice those occurrences which, at each period, 

 have exerted a decisive influence on the intellectual efforts 

 of man, and on a more enlarged and extended view of the 

 universe. Such have been, to the nations settled round the 



