1267
Roger Bacon completes his work Opus Majus and sends it to Pope Clement IV, who had requested it be written; the work contains wide-ranging discussion of mathematics, optics, alchemy, astronomy, astrology, and other topics, and includes what some believe to be the first description of a magnifying glass. Bacon also completes Opus Minus, a summary of Opus Majus, later in the same year. The only source for his date of birth is his statement in the Opus Tertium, written in 1267, that "forty years have passed since I first learned the alphabet". The 1214 birth date assumes he was not being literal, and meant 40 years had passed since he matriculated at Oxford at the age of 13. If he had been literal, his birth date was more likely to have been around 1220.