Lemma III
Si annulus, Terra omni reliqua sublata, solus in orbe Terræ motu annuo circa Solem ferretur, & interea circa axem suum, ad planum Eclipticæ in angulo graduum 23½ inclinatum, motu diurno revolveretur: idem foret motus Punctorum Æquinoctialium sive annulus iste fluidus esset, sive is ex materia rigida & firma constaret.