(The). That is, the Firmament. According to the Ptolemaic System, the earth is surrounded by nine spheres. These spheres are surrounded by the Primum Mobile (or First Moved); and the Premium Mobile is enveloped by the empyrean, or abode of deity.
They pass the planets seven, and pass the fixt. And that crystalline sphere whose balance weighs The trepidation talked, and that first moved.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894