26th January

On this day in 1697, Isaac Newton received Johann Bernoulli's brachistochrone problem. According to Newton's biographer Conduitt, he solved the problem in an evening after returning home from the Royal Mint. Newton:
... in the midst of the hurry of the great recoinage, did not come home till four (in the afternoon) from the Tower very much tired, but did not sleep till he had solved it, which was by four in the morning.