A late 18th century gold mounted carnelian intaglio seal depicting Sir Isaac Newton, later adapted to a ring, the intaglio depicting the sitter in profile ‘a sinister’, with comet/star behind, mounted in polished gold closed back setting, later mounted to a plain broad shank, ring size N. £400-£600

The image of Sir Isaac Newton (1643-1727) is after the Wedgwood medallion modelled by William Hackwood.
Literature:
Reilly & Savage: Wedgwood, the Portrait Medallions, pub. 1973, p.58.