Where the telescope ends, the microscope begins.
   — Victor Hugo, Les Misérables, 1862

A glass lens. It’s nothing more than a curved piece of glass. So simple. So familiar. It’s changed the way we perceive the world.

In 1608, when Dutch spectacle maker Hans Lippershey held up two lenses, one behind the other, he was surprised to see a close-up view of a distant steeple. He had discovered a powerful tool. Soon, people all over Europe were putting lenses in tubes to make “spy glasses.” Within a year, Italian scientist Galileo Galilei had made one, too. He used his instrument, which he called a telescope, to study the night sky. The moon, he saw, had rugged mountains; the Milky Way, countless stars.

Like the telescope, the first microscope had two lenses. Then, in 1674, Dutch naturalist Antonj Van Leeuwenhoek built the most powerful microscope of his time, using a single, spherical lens. He inspected a drop of water. It was teeming with life. His tiny lens had revealed that nature was far more complex than anyone had dreamed.

How does a lens bend light?

This lens is slowing down the light waves entering it from the air. The lens is denser than air—it slows light. As each wave front meets the curved surface of the lens, some parts slow down first, causing the light to bend, or refract. When the wave front leaves the lens, some parts speed up first, and the light bends again.

How a complex microscope works

The first microscopes were natural outgrowths of telescopes and had two lenses. British scientist Robert Hooke's 17th-century compound microscope, like modern microscopes, has three lenses. An objective lens gathers light and forms an image. A field lens and an eyepiece lens then magnify the image.

The Corning Museum of Glass
This article was originally published in Innovations in Glass, 1999, pp. 28–29.

Published on October 25, 2011