(3 syl.). The Crystalline sphere. According to Ptolemy, between the “primum mobile” and the firmament or sphere of the fixed stars comes the crystalline sphere, which oscillates or has a shimmering motion that interferes with the regular motion of the stars.
They pass the planets seven, and pass the `fixed' And that crystalline sphere, whose balance weighs The trepidation talked (of).
Milton: Paradise Lost, iii.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894