Ken Schwartz, age 11, of Grand Rapids, MI., for his question:
WHEN WAS THE MICROSCOPE INVENTED?
Engravers probably used glass globes filled with water as magnifying glasses at least 3,000 years ago, and these were probably the world's first microscopes. And the Romans may have made magnifying lenses from rock crystal in the ancient days.
But glass lenses similar to the type used in today's microscopes were not introduced until the late A.D. 1200s.
Historians give credit to a Dutch spectacle maker named Zacharian Janssen for discovering the principle of the compound microscope in about 1590. Then in the mid 1600s, a Dutch amateur scientist named Anton Van Leeuwenhoek made microscope lenses that could magnify up to 270 times.
Van Leeuwenhoek also built simple microscopes more powerful than the compound microscopes of his day. He was the first person to observe microscopic life and record his observations.
Few imporovements in the microscope occurred until the early 1800s when better glass making methods produced lenses that provided undistorted images.
C.A. Spencer, an optical instrument manufacturer of Canastota, New York, made the first American microsocpes about 1838.
Today the microscope ranks as one of the most important tools of science. With it, researchers first saw the tiny germs that cause disease. The microscope reveals an entire world of organisms too small to be seen by the unaided eye.
An optical microscope has one or more lenses that bend the light rays shining through the specimen. The bent light rays join and form an enlarged image of the specimen.
The simplest optical microscope is a magnifying glass.
German scientists demonstrated the first electron microscope in 1931 .
Scientists use a number and the abbreviation "X" to indicate the image of an object magnified by a certain number of times or a lens that magnifies by that number of times. A 10X lens, for example, magnifies an object by 10 times.
Greater magnification can be achieved by using a compound microscope. Such an instrument has two lenses, an objective lens and an ocular, or eyepiece, lens. The objective lens, often called simply the objective, produces a magnified image of the specimen, just as an ordinary magnifying glass does.
The ocular lens, also called the ocular, then magnifies this image, producing an even larger image.
Many microscopes have three standard objective lenses that magnify by 4X, 10X and 40X. When these objective lenses are used with a 10X ocular lens, the compound microscope magnifies a specimen by 40X, 100X or 400X.