save one's bacon

1. n.
   the police; a police officer. (See also pig.) : Keep an eye out for the bacon.

Our Living Language  : Roger Bacon was something of a Renaissance man before there was a Renaissance. Over the course of his long life, his energetic research would lead him to study everything from languages to mathematics to optics. He is most remembered for his insistence on the importance of pursuing fruitful lines of scientific research through experimentation. His writings describe countless experiments; while the majority were probably never performed by him, the profusion alone of experimental ideas is nothing short of astounding. His own laboratory work dealt primarily with alchemy, optics, and mechanics. He was among the first to apply geometric and mathematical principles to problems in optics and the behavior of light, allowing him to make important observations on reflection and refraction. His interest in mechanics led him to describe flying machines and other devices that had not yet been invented. He was the first person in the West to come up with a recipe for gunpowder, and he suggested reforms to the calendar, which would ultimately be implemented hundreds of years later. His novel ways of pursuing knowledge were sometimes viewed with suspicion, resulting at one time in imprisonment; but he bravely resisted all strictures on his intellectual life, even when that meant having to write and work in secret.