In march 1693 Fatio de Duillier had been invited by Newton to rejoin him in Cambridge at Newton's expense, and on 11 April (apparently in reply to this invitation) Fatio wrote:

Thereafter, the intimate and frequent correspondence between the two men ceases; the following summer was that of Newton's mental illness. We have no evidence as to what passed when Newton admitted his friend, at Cambridge, to the privacy of his manuscripts, nor subsequently do we have any record of how he reacted to Fatio's dramatic displays, first in private and finally in public, of his admiration for Newton and his conviction that Leibniz had stolen the calculus from Newton. If letters were exchanged between the two men, or if (as is unlikely enough, in fact) Newton disclosed his personal judgment of Fatio to others, the documents have failed to survive.