The electron microscope uses beams of electrons in place of beams of light.
The superiority of the electron microscope over the optical microscope depends on the fact that fast-moving electrons have a wave length a 100,000 times smaller than the wave length of visible light.
The magnifying power of the electron microscope is about 200 times that of the very best optical microscope.
The magnifying power of an optical microscope is thus limited by the fact that objects cannot be distinguished unless they are somewhat larger than the waves of light reflected from them.
Contemporary electron microscopes are capable of 2 million-power magnification.
In 1932 Ernst Ruska, a German physicist, constructed an electron microscope. He allowed a beam of electrons to be reflected from an object. Since electrons are charged they can be controlled by electric and magnetic fields.) The reflected electrons were directed through a magnetic field and then focused on a screen (as electrons are focused on a televisión screen to make a visible image) or on a photographic plate so that the image be recorded.
The major disadvantage of the transmission electron microscope is the need for extremely thin sections of the specimens, typically about 100 nanometers.
