Sentence:  Far more extravagant ("insanior") yet is the idea of the whirling of the supposititious <WSD>"primum mobile</WSD>", which is still higher, deeper, more immeasurable; and yet this incomprehensible <WSD>"primum mobile</WSD>" would have to be of matter, of enormous altitude, and far surpassing all the creation below in mass, for else it could not make the whole universe down to the earth revolve from east to west, and we should have to accept a universal force, an unending despotism, in the governance of the stars, and a hateful tyranny. 
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.