In 1771, misfortune struck Euler again, when a cataract in his left eye robbed him of his sight entirely. Incredibly, this did not seem to slow him at all. In fact, during his remaining thirteen years, his publishing output accelerated. Of the 886 books and articles he produced in his lifetime - on topics including mathematics, philosophy, mechanics, electricity, astronomy, optics, and music - half of them were completed after total blindness!