The new Scanning Electron Microscopes are huge, many times larger than even the most powerful standard microscopes.
Nobody minds that they are so big, however, because they are very powerful. The Scanning Electron Microscope “sees” 10,000 times more than even the finest standard micropcope.
By gathering light and focusing it with a system of mirrors and lenses, a normal microscope can enlarge a specimen 2,000 times. An electron microscope, called an SEM, can magnify the same specimen 20 million times.
An SEM bombards its specimen with a beam of electrons 1 million times. The electron flow is aimed and focused by magnetic lenses, and the picture they produce is seen at the ground level of the 20-foot-tall device.
Scientists have to look at the picture through an 8-inch-thick piece of leaded glass. The glass protects the scientists from the deadly X-rays produced by all the electrons.
In 1931, German engineers Ernst Ruska and Max Knoll built the first electron microscope prototype.