Profession: scientist

One of the most influential scientists and mathematicians ever, Newton was a key figure in the scientific revolution. Barrow taught him at Cambridge and recommended him as his own successor. Halley was one of his keenest supporters – his zealous enthusiasm encouraged Newton to publish his Principia Mathematica. Newton met Huygens in London, told his former friend Flamsteed to stick to observation (not theory), and tried to discredit Leibniz (corresponding via Oldenburg as intermediary). He corresponded with Boyle about alchemy, Pepys about gambling odds, and Hooke (whose criticisms hurt) about optics. Cheselden advised against operating when Newton was dying.

Playfair is known, not for original discoveries, but for his clear expounding of theories (especially Hutton’s). Hutton was a close colleague — Playfair, Black and he often spending evenings together, including at the Oyster Club, where other members (and friends of Playfair) included Smith and Ferguson, whom Playfair held a joint professorship with. Playfair encouraged Somerville, investigated Edinburgh geology with Nasmyth, and met his lifelong friend Maskelyne (who got him to publish his first mathematical paper, and introduced him to London colleagues) by visiting and helping with his experimental measuring of mass at Schiehallion.