 Given the dramatic increase in resolving power over light, we'll use electrons instead of photons to illuminate the objects. The most common electron microscope is called a scanning electron microscope, SEM. Here's how they work. An electron gun heats up a metal, such as tungsten, to a temperature where it releases its electrons. An anode, with a large charge, accelerates the electrons to a very high speed to improve their resolving power. Where glass lenses are used in an optical microscope to bend and focus the light, electron microscopes use powerful magnetic and electric field generators, like this one, to bend and focus the electron beam. Scanning coils are then used to focus the electrons onto a tiny spot on the specimen and move it across for a full picture of the surface. Different wavelengths penetrate the surface of the specimen and provide information on its structure. Here we are detecting the secondary electrons that define the surface of the specimen. The entire operation is done in a vacuum. The results are fed into a computer for processing and color additions. So let's take a look at what we can see with electron microscopes. Here's an interesting look at bees through an electron microscope magnified 150 times. As you'll see, the resolving power of the electron microscope provides images with dramatic clarity and detail not possible with optical tools. Because it's not light, there is no color associated with the images. Color can be added after the images created by the electron microscope. Here's what a sheet of paper looks like at 1,000 magnification. Here's a human hair magnified 1,200 times. This is a micrograph of red blood cells clumped together with fibrin to form a blood clot. This colored SEM monograph shows the rods and cones in the retina of the eye. The rods are tan and measure around 1 micrometer in diameter. The cones are green and measure around 8 micrometers in diameter. A nerve fiber is a thread-like extension to a nerve cell. Here's a colored scanning electron micrograph of malignated nerve fibers. The malign sheath is gray, the nerve inside is pink, and the connective tissue is yellow. Here's the texture of the skin of a spider magnified 12,000 times. The most powerful electron microscopes can resolve images as small as carbon atoms. Here's a sheet of carbon atoms with each atom around 0.14 nanometers in diameter. That's around a billion times smaller than the human hair we saw earlier. Given the electron wavelength, this is about as good as we can do. In this segment, we've gone from what we can see with the human eye to what we can see with optical microscopes to what we can see with electron microscopes. In our next segment, we'll take a closer look at atoms and their subatomic particles.