Oh, the other weird thing about this is that even though the "external" catalog information on makingscience.royalsociety.org and the "internal" catalog information penned on page 2 of the letter both describe it as a letter written to Leibniz, and sent to Leibniz, the text of the letter itself refers to Leibniz only in third person, and refers to some other individual in the second person. But it does make (oblique) requests of Leibniz, e.g.
> I question not but Mr Leibnitz may have many of those specimens by him and therefore I doe heartily wish you could prevail wh him to Communicate some of those which would be a means to persuade severall yet incredulous of the possibility of such a Science.
I suppose it could have been written to Leibniz's personal secretary, or some such. If it weren't for all the catalog data I'd assume it was written to some close colleague of Leibniz instead. Anybody want to track down a plausible explanation/mechanism here?
I was going to bring up the same claim—of it being a "Letter, from Robert Hooke to Gottfried Wilhelm Leibniz". It's clearly not written with that intent.
While reading, I first took it to be a journal entry. The penmanship also supports this. But the second person "you" at the end is a confounding detail. A journal entry in the form of a letter to himself is possible, but doesn't seem plausible.
The word you've labelled "[deviate?]" in your copy is definitely not "deviate" in the manuscript. I'm certain that the first letter is "R", and the second to last letter probably a "d" followed by "e" (compare to "undenyable" and "persuade"). The letter following "R" could be "i", but really could be anything. It's unfortunate that it's not as straightforward as just crafting a regex and grepping at /usr/share/dict/words, because whatever Hooke meant, it's likely to be an archaic spelling. "Recede" spelled as "Ricede" works grammatically, but I don't think that's it, either.
FYI I agree with you on that word: letter by letter it looks to me like "Roeade", but I can't figure out what English word that would be, either.