Robert Boyle once wrote in one of his papers:
That, then, which I chiefly aim at is to make it probable to you by experiments (which I think hath not yet been done) that almost all sorts of qualities, most of which have been by the Schools either left unexplicated, or generally referred to I know not what incomprehensible substantial forms, may be produced mechanically - I mean by such corporeal agents as do not appear either to work otherwise than by virtue of the motion, size, figure, and contrivance, of their own parts
-- Selected Philosophical Papers of Robert Boyle [On Google Books]
I have several difficulties regarding the meaning and grammar of above-mentioned passage:
The best way I can understand I know not is as a parenthetical phrase. Is that correct? Why not I don't know? Even so I could not make a proper sense of the sentence. There should be something referring in the phrase generally referred to I know not what incomprehensible substantial forms to the outer which, but here it seems that there is no such reference.
In the next sentence we read such corporal agents as do not .... I think there is a subject omitted in this case: such corporal agents as that which do not .... Is that correct? Is there a general rule regarding this omission?