Sentence:  A <WSD>"primum mobile</WSD>", therefore, being essential to the celestial mechanism, the same may be proved geometrically to originate in a "solar repulsion", or in a repulsive force produced by whatsoever cause, and emanating spontaneously from the central luminary; [...] 
Meaning of the word marked with <WSD> tags:  The outermost celestial sphere of the heavens in Ptolemaic astronomy, which was believed to cause all the inner spheres to rotate.