208 cosmos. 



down."* We find nothing of this view of the structure of 

 the universe, this assumption of dark cosmical bodies which 

 fall upon our earth, in the doctrines of the old Ionic schools, 

 from Thales and Hippocrates to Empedocles.f The impres- 

 sion made by the occurrence of nature in the 78th Olympiad 

 appears to have powerfully called forth the idea of the fall 

 of dark masses. In the more recent Pseudo-Plutarch (Plac, 

 ii., 13), we read merely that the Milesian Thales considered 

 " all stars to be earthy and fiery bodies (yedodi] teat t^7ri;pa)." 

 The endeavors of the earlier Ionic physiology were directed 

 to the discovery of the primitive cause of all things, forma- 

 tion by mixture, gradational change and transition of one 

 kind of matter into another : to the processes of genetic de- 

 velopment by solidification or dilution. The revolution of 

 the sphere of the heavens, " which holds the Earth firmly in 

 the center," was already conceived by Empedocles as an act- 

 ively moving cosmical force. Since, in these first attempts 

 at physical theories, the ether, the fire-air (and, indeed, fire 

 itself), represents the expansive force of heat, so the idea of 

 the propelling revolution rending fragments from the Earth 

 became connected with the lofty region of the ether. There- 

 fore Aristotle calls (Meteorol, i., 339, Bekker) the ether "the 

 eternally moving body,"$ as it were the immediate substra- 

 tum of motion, and seeks for etymological reasons for this as- 

 sertion. On this account, we find in the biography of Ly- 

 sander " that the relaxation of the centrifugal force causes 

 the fall of celestial bodies ;" as also in another place, where 

 Plutarch, evidently alluding again to opinions of Anaxago- 

 ras, or Diogenes of Apollonia (De Facie i?i Orbe Lunce, p. 

 9-23), puts forward the assertion "that the Moon would fall 

 to the Earth like a stone in a sling if its centrifugal force 



* This remarkable passage (Plut., Lys., cap. xii.), literally translated, 

 runs thus : " But there is another and more probable opinion, which 

 holds that falling stars are not emanations or detached parts of the el- 

 ementary fire, that go out the moment they are kindled, nor yet a quan- 

 tity of air bursting out from some compression, and taking fire in the 

 upper regions; but that they are really heavenly bodies, which, from 

 some relaxation of the rapidity of their motion, or by some irregular 

 concussion, are loosened and fall, not so much upon the habitable part 

 of the globe as into the ocean, which is the reason that their substance 

 is seldom seen." 



t With regard to absolutely dark cosmical bodies, or such in which 

 the light-process ceases (periodically?); as to the opiuions of moderns 

 (Laplace and Bessel) ; and Bessel's observation, confirmed by Peters in 

 Konigsberg, of a variability of the proper motion of Procyon, see Cosmos, 

 vol. iii., p. 1G4-166. t Compare Cosmos, vol. iii., p. 31-33. 



