The wonderful, talented, and fabulous Jennifer Ouellette (with whom, though I know she reads this blog, I would never, of course, try to curry favor by calling her wonderful, talented, and fabulous -- but I will admit to having an animated crush on Jen-Luc Piquant) of Cocktail Party Physics has written a fun essay on the history of calculus. Yes, I said "fun". She writes poetically about the beauty and internal wonder of epsilon, the infinitesimal jump from one point to the next in a function that makes calculus possible. If you love math, you should read her essay, and if you hate math, you should really read it, because she might change your mind.
And at the end, she posts a little math trick, which I unceremoniously dissect in the comments.