194 COSMOS. 



This latter mode of proceeding characterizes the investiga- 

 tions of Ptolemy on the refraction of rays in their passage 

 through media of unequal density. Ptolemy caused the rays 

 to pass from air into water and glass, and from water into 

 glass, under different angles of incidence, and he finally ar- 

 ranged the results of these physical experiments in tables. 

 This measurement of a physical phenomenon called forth at 

 will, of a process of nature not dependent upon a movement 

 of the waves of light (Aristotle, assuming a movement of the 

 medium between the eye and the object), stands wholly iso- 

 lated in the period which we are now considering.* This age 

 presents, with respect to investigation into the elements of na 

 ture, only a few chemical experiments by Dioscorides, and, as 

 I have already elsewhere noticed, the technical art of collect- 

 ing fluids by the process of distillation. t Chemistry can not 

 be said to have begun until man learned to obtain mineral 

 acids, and to employ them for the solution and liberation of 

 substances, and it is on this account that the distillation of sea 

 water, described by Alexander of Aphrodisias under Caracalla, 

 IS so worthy of notice. It designates the path by which man 

 gradually arrived at a knowledge of the heterogeneous nature 

 of substances, their chemical composition, and their mutual 

 aiiinities. 



The only names which we can bring forward in connection 

 with the study of organic nature are the anatomist Marinus ; 

 Rufus of Ephesus, who dissected apes, and distinguished be- 

 tween nerves of sensation and of motion ; and Galen of Pcr- 

 gamus, who eclipsed all others. The natural history o^ uii- 

 mals by ^lian of Prseneste, and the poem on fishes by Op- 

 pianus of Cilicia, contain scattered notices, but no facts based 

 on personal examination. It is impossible to comprehend how 

 the enormous multitudes of elephants, rhinoceroses, hippopot- 

 amuses, elks, lions, tigers, panthers, crocodiles, and ostriches, 

 which for upward of four centuries were slain in the Roman 



whether a particular result has sprung from a phenomenon purposely 

 called forth or accidentally observed. Where Aristotle {De Casio, iv., 

 4) treats of the weight of the atmosphere, which, however, Ideler ap- 

 pears to deny {Meteorologia veterum GrcECorum et Romanorum, p. 23), 

 he says distinctly, ** an inflated bladder is heavier than an empty one." 

 The experiment must have been made with condensed air, if actually 

 tried. 



* Aristot., De Anima., ii., 7 ; Biese, Die Philosophic des AristoL, bd. 

 ii., s. 147. 



t Joannis {Philoponi) Grammatici, in libr. De Generat., and Alex- 

 andri Aphrodis., in Meteorol. Comment. (Venet.. 1527), p. 97, b. Com- 

 pare my Examen Critique, t. ii., p. 306-312 



