 Hello, and welcome to the first segment of our video book How Small Is It? Where we'll examine the size of things, from where we see them around us, everyday things down to the smallest things that exist. For that, we'll be using a meter stick. A meter is roughly the same size as a yard. It's just three inches longer. In addition to how much space an object might take up, we're going to be looking at how little its mass and energy might be. For that, take a look at the apple. A hundred grams, roughly. And to raise a hundred gram apple, one meter, is the energy of one jewel. We'll get much smaller than that as we move into additional segments. We see things because light bounces off an object and into our eye. But the smaller things get, the harder they are to see. A human hair is about one-tenth of a millimeter, that's a millimeter is a thousand of a meter. In order to see things this smaller, or smaller, we use lenses, like this lens here, to get a better look at the size of a hair. But how far can we go, bending light? And just how small can things get? We'll be using microscopes, various kinds of microscopes, to see down to the nanometer level. A nanometer is one billionth of a meter. There are twenty-five million four hundred thousand nanometers in an inch. So let's get started with optical microscopes.