Finally we come to Newton's reply of 5th February 1676. He says Hooke has ``done what becomes a true Philosophical spirit'' and that ``there is nothing wch I desire to avoyde in matters of Philosophy more than contention, nor any kind of contention more than one in print.'' In response to Hooke's compliment that Newton was the fittest person to continue his investigations, he begins:
you defer too much to my ability for searching into this subject. What Des-Cartes did was a good step. You have added much several ways, & especially in taking ye colours of thin plates into philosophical consideration. If I have seen further it is by standing on ye shoulders of Giants. But I make no question but you have divers very considerable experiments besides those you have published, & some it's very probable the same wth some of those in my late papers. Two at least there are wch I know you have observed.
The tone is certainly conciliatory and significantly Newton praises Hooke for beginning and publishing the study of phenomena of thin plates, just as he did in the letter to Oldenburg on 21st December 1675, and just as Hooke insisted on in his letter to Newton (and remember this is the only claim Hooke makes in that letter.) It seems that all three letters agree over this issue and both Newton and Hooke imply the other has achieved more than they claim credit for. This flatly contradicts suggestions that they are damning each other with faint praise or implying the other's work is unimportant.
In context, it seems that the ``Giants'' can only be Descartes and Hooke. This is certainly the implication of this passage at face value and Newton mentions no one else in the corresponding passage in his letter to Oldenburg. I find the idea that the word ``Giants'' is meant to exclude Hooke on the grounds of his height implausible (It is a plural after all!)
It has also been suggested that ``Giants'' is meant as cruel irony or slight. It is certainly an exageration but I see no evidence that this is intended as sarcasm rather than an extravagant compliment. Westfall dismissed this with two of his distinctive comments: ``As Newton said once before in regard to Hooke, he avoided oblique thrusts. When he attacked, he lowered his head and charged'' (http://www.isaacNewton.org.uk/books/NR p274 n106) referring to Newton's letter to Oldenburg on 11th June 1672, again in response to criticisms from Hooke. He said he had avoided ``oblique & glancing expressions'' to which Westfall says ``That is, he employed the broadsword instead of the rapier.'' (http://www.isaacNewton.org.uk/books/NR p247) Whatever else one says about the ``Giants'' letter of 5th February 1676, obvious slashes from Newton's broadsword are not visible.
After accepting Hooke's offer of a private correspondence, Newton initiates it by repeating a verbal offer to observe the transit of a star near the zenith, in Cambridge. He even weaves it into the conventional ending of a letter by saying ``If therefore you continue in ye mind to have it observed, you may by sending your directions command Your humble Servant Is. Newton.''
Despite this, no reply from Hooke has been found. Hall calls this ``astonishing insensitivity'' (http://www.isaacNewton.org.uk/books/ARHALL p139) but presumably Newton, deep in alchemy and theology by this time, was less concerned.