᾽Εμπεδοκλῆς στερέμνιον εἶναι τὸν οὐρανὸν ἐξ ἀ& 153·ρος συμπαγέντος ὑπὸ πυρὸς κρυσταλλοειδῶς, τὸ πυρῶδες καὶ ἀερῶδες ἐν ἑκατέρῳ τῶν ἡμισφαιρίων περιέχοντα.  (Plutarch περὶ τῶν ἀρεσκόντῶν τοῖς φιλοσόφοις, ii. 11.)  Pliny (Hist. Nat. xxxvii. 9) says that crystal is made “gelu (vide Sir T. Browne, Vulgar Errors, ii. 1) vehementiore concreto…glaciem que esso certum est; unde et nomen græci dedere.”  So Seneca, Quæst. Nat. iii. 25.  Diodorus Siculus, however, asserts it “coalescere non a frigore sed divini ignis potentia.”  (Bibl. ii. 134.)