168 COSMOS. 



ancients, w and their ideas of the solidification of fluids, have 

 referred directly to cold and ice ; but the affinity between 

 KpixrTa\\os, Kpvos, and AcpvoraiVo), as well as this comparison 

 with the most transparent of all bodies gave rise to the 

 more definite assertion that the vault of heaven consisted of 

 ice or of glass. Thus we read in Lactantius : " Ccelum aerem 

 glaciatum esse," and " vitreum coslum." Empedocies un- 

 doubtedly did not refer to the glass of the Phoenicians, but 

 to air, which was supposed to be condensed into a transparent 

 solid body by the action of the fiery ether. In this comparison 

 with ice, (KpvoraXXos) the idea of transparency predominated ; 

 no reference being here made to the origin of ice through cold, 

 but simply to its conditions of transparent condensation. 

 While poets used the term crystal, prose writers (as found in 

 the note on the passage cited from Achilles Tatius, tl^e com- 

 mentator of Aratus) limited themselves to the expression 

 crystalline or crystal-like, Kpvo-raXXoeiS?;?. In like manner 

 Kayos (from 7ri]yw<r6ai, to become solid), signifies apiece of ice 

 its condensation being the sole point referred to. 



The idea of a crystalline vault of heaven was handed down 

 to the middle ages by the Fathers of the Church, who believed 

 the firmament to consist of from 7 to 10 glassy strata, incasing 

 one another like the different coatings of an onion. This sup- 

 position still keeps its ground in some of the monasteries of 



things, whatever they may be, have a natural and proper light 

 of their own," (the region of self-luminous stars) "which so 

 impends over the sphere of the sun with all its fire, that those 

 zones of heaven which are far from the sun are oppressed by 

 perpetual cold." My reason for entering so circumstantially 

 into the physical and meteorological ideas of the Greeks and 

 Romans, is simply because these subjects, except in the works 

 of Ukert, Henri Martin, and the admirable fragment of the 

 Meteorologia Veterum of Julius Ideler, have hitherto been very 

 imperfectly, and for the most part superficially, considered. 

 M The ideas that fire has the power of making rigid, ( Aristot. 



