The lost portrait of Robert Hooke?

This letter considers the 'Portrait of a Mathematician' attributed to Mary Beale in the 1680s as a likely candidate for a portrait of Robert Hooke made during his lifetime. It closely matches the physical descriptions of Hooke made by his biographers who knew him, Richard Waller (d. 1715) and John Aubrey (1626-1697). The portrait contains a remarkable diagram, as well as its mechanical analogue, demonstrating the elliptical orbit of a body under constant force similar to an unpublished, unfinished 1685 manuscript by Hooke. It also contains a landscape, which is likely to be Lowther Castle and its associated church. Hooke provided designs for the Lowther castle church renovations completed in 1686. The portraitist, Mary Beale, knew Hooke and was very familiar with the Lowther family, who commissioned 30 portraits from her. The diagram and armillary sphere in the portrait establish Hooke's contribution to the theory of gravity. Their presence may have been one of the reasons the portrait was not purchased and kept by the Royal Society. It might have diminished the legacy of Isaac Newton.