Now we must say something about the nature of the firmament, and why it received the order to hold the middle place between the waters.  Scripture constantly makes use of the word firmament to express extraordinary strength.  “The Lord my firmament and refuge.” Ps. xviii. 2, LXX.  “I have strengthened the pillars of it.” Ps. lxxv. 3, LXX.  “Praise him in the firmament of his power.” Ps. cl. 1. LXX.  The heathen writers thus call a strong body one which is compact and full, ναστός (fr. νάσσω, press or knead)=close, firm.  Democritus used it as opposed to κενόν, void.  Arist. fr. 202. to distinguish it from the mathematical body.  A mathematical body is a body which exists only in the three dimensions, breadth, depth, and height.  A firm body, on the contrary, adds resistance to the dimensions.  It is the custom of Scripture to call firmament all that is strong and unyielding.  It even uses the word to denote the condensation of the air: He, it says, who strengthens the thunder. Amos iv. 13, LXX.  Scripture means by the strengthening of the thunder, the strength and resistance of the wind, which, enclosed in the hollows of the clouds, produces the noise of thunder when it breaks through with violence. Pliny (Hist. Nat. ii. 43) writes:  “Si in nube luctetur flatus aut vapor, tonitrua edi:  si erumpat ardens, fulmina; si longiore tractu nitatur, fulgetra.  His findi nubem, illis perrumpi.  Etesse tonitrua impactorum ignium plagas.”  cf. Sen., Quæst. Nat. ii. 12.  Here then, according to me, is a firm substance, capable of retaining the fluid and unstable element water; and as, according to the common acceptation, it appears that the firmament owes its origin to water, we must not believe that it resembles frozen water or any other matter produced by the filtration of water; as, for example, rock crystal, which is said to owe its metamorphosis to excessive congelation, ᾽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.) or the transparent stone i.e. the “Lapis Specularis,” or mica, which was used for glazing windows.  cf. Plin., Ep. ii. 17, and Juv., Sat. iv. 21. which forms in mines. Mica is found in large plates in Siberia, Peru, and Mexico, as well as in Sweden and Norway.  This pellucid stone, if one finds it in its natural perfection, without cracks inside, or the least spot of corruption, almost rivals the air in clearness.  We cannot compare the firmament to one of these substances.  To hold such an opinion about celestial bodies would be childish and foolish; and although everything may be in everything, fire in earth, air in water, and of the other elements the one in the other; although none of those which come under our senses are pure and without mixture, either with the element which serves as a medium for it, or with that which is contrary to it; I, nevertheless, dare not affirm that the firmament was formed of one of these simple substances, or of a mixture of them, for I am taught by Scripture not to allow my imagination to wander too far afield.  But do not let us forget to remark that, after these divine words “let there be a firmament,” it is not said “and the firmament was made” but, “and God made the firmament, and divided the waters.” Gen. i. 7.  Hear, O ye deaf!  See, O ye blind!—who, then, is deaf?  He who does not hear this startling voice of the Holy Spirit.  Who is blind?  He who does not see such clear proofs of the Only begotten. With Christian associations it is startling to read at the end of the Timæus that the Cosmos is the εἰκὼν τοῦ Θεοῦ, or, according to another reading, itself Θεός,… μονογενὴς ὤν.  “Let there be a firmament.”  It is the voice of the primary and principal Cause.  “And God made the firmament.”  Here is a witness to the active and creative power of God.