Microscopes have been used to observe tiny objects for thousands of years. The most common type, the optical microscope, magnifies these objects with lenses that bend and focus the light.

When an object is viewed through a magnifying lens, the light is bent towards the center. When the bent light reaches the eye, the object appears bigger than it really is. This was first noted in ancient times with objects viewed through water and pieces of crystal.

Early scientists used drops of water suspended from small holes in wood or metal frames. By the Renaissance, the water had been replaced with glass lenses. In the 17th Century, Dutch scientist Antonie van Leeuwenhoek made the first observations of microscopic organisms with a high-quality lens mounted between brass plates.

In the 16th and 17th Centuries, European scientists began using several lenses together to improve their observations, creating the compound microscope. In a compound microscope the image produced by the first lens is further magnified by a second lens and that image is magnified by a third .

In 1931, German scientist Ernst Ruska developed the first electron microscope. Electron microscopes focus a beam of electrons through a magnetic lens. Since electrons have smaller wavelengths than light, higher magnification is possible, permitting the observation of the submicroscopic and subatomic world.