According to Ptolemy, there are five heavens, the last of which is pure elemental fire and the seat of deity; this fifth heaven is called the empyrean (from the Greek en-pur, in fire). (See Heaven.)
Now had the Aln ighty Father from above, From the pure empyrean where He sits High throned above all height, bent down his eye.
And again, book vi. 833:
“The steadfast empyrean shook without.”
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894