Raqi'ah , "the expanse stretched out as a curtain" over the earth (Isaiah 40:22; Psalms 104:2), resting on the mountains as its pillars (the language is phenomenal, as indeed necessarily is that of even men of science often): Job 26:11. It was the reservoir of rain and snow, which poured through its opened "windows" or "doors" (Genesis 7:11; Isaiah 24:18; Psalms 78:23). It includes the atmosphere immediately round the earth, in which the birds fly, and which bears up the clouds (Genesis 1:6-7; Genesis 1:20; in Genesis 1:14 it also comprises the region in which the sun, moon, and stars are seen).
"Firmament" (from the Vulgate: firmamentum; Septuagint: stereooma ) is derived from firmness; but the Hebrew expresses no such notion, as if Moses thought the sky a hard firm vault, in which the heavenly bodies were fixed. The sky in Job 37:18 is termed "strong, as a molten looking glass," namely, a polished copper mirror. But it is not the solidity, but the transparent clearness and the smiling brightness, which is the point of comparison. Otherwise, how could birds fly in a solid? The language is figurative and phenomenal. In Ezekiel 1:26 the throne is seen above the "firmament," therefore the firmament must be transparent.