What`s a microscope? Van Leeuwenhoek Hooke Optical microscopes

Saturday, August 22, 2009
What’s a microscope?
A microscope (Greek: mikros “small” and skopein
“see”) is a scientific tool invented to view objects
that are too tiny to be seen by the naked eye. The
observation of small objects under a microscope
is the science of microscopy.
There are many kinds of microscopes. They can
generally be divided into three classes: optical
theory microscopes, electron microscopes,
and scanning probe microscopes. The optical
microscope came first, and it is the most common
kind in use today. It contains one or more lenses
that produce an enlarged image of objects placed
in the focal plane of the lenses.
The work of Antonie Van Leeuwenhoek advanced
early versions of the microscope during the
1670s, but the first true microscope was made
in Middelburg, the Netherlands, around 1595.
Three different eyeglass makers have been
given credit for the invention of the microscope,
including Hans Lippershey (who also developed
the telescope); Sacharias Jansen; and his son,
Zacharias. Giovanni Faber gets credit for the
name “microscope” — he gave that moniker to
Galileo Galilei’s compound-microscope invention
in 1625, although Galileo had called it the
occhiolino (little eye).
LIGHT
SOURCE
LENS
Van Leeuenhoek made more than 200
microscopes. His drawings included plant
cells and cross sections in incredible detail.
SUBJECT
Van Leeuwenhoek
GLASS SLIDE
LENS
Optical microscopes
LENS
EYEPIECE
Optical microscopes work by using
various lenses to magnify an object (a
sample). The image is generated by
the passage of light waves through the
sample.
Most optical microscopes use visible
wavelengths of light and are the simplest
and most widely used type of microscope.
Optical microscopes typically use
refractive glass (sometimes plastic or
quartz) to focus light into either the eye or
another light detector such as a camera.
Mirror-based optical microscopes operate
in much the same way.
Typical magnification is up to 1,500x,
with a resolution limit of about 0.2
micrometers. When more than one
lens is used, they are called compound
microscopes.
Hooke
An English natural philosopher
who played a key role in the
scientific revolution with his
experimental and theoretical
work, Robert Hooke (16351703) published Micrographia in
1665; it described his microscopic
and telescopic observations.
He was the first to use the word
“cell” to describe biological
organisms. Hooke’s gold-andleather compound microscope
is on display at the National
Museum of Health and Medicine in
Washington, DC.
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Distributed by United Feature Syndicate, Inc.
Hooke’s drawings in Micrographia
included a flea, plant cells and
other microorganisms.
Antonie Philips Van Leeuwenhoek
(1632-1723) lived in Delft, the
Netherlands. Considered the first
microbiologist, he is best known for
his improvements on the microscope
and work that led to the science of
microbiology.
Van Leeuwenhoek made many
microscopes (by hand) and was the
first to observe and describe single-cell
organisms. He called his discoveries
“animalcules,” but we call them
“microorganisms” today. He recorded
microscopic observations of muscle
fibers, bacteria, spermatozoa and blood
flow through the capillaries.
Van Leeuwenhoek’s interest in
microscopes stemmed from his
knowledge of glassmaking. One of his
most significant technical developments
was the ability to create lenses from
very small spheres of glass. To do this,
he placed a rod of glass into a hot
flame and pulled it apart to create two
very thin strings of glass. When the end
of the string re-entered the flame, a
small perfect sphere would form. These
spheres became microscope lenses.
The smallest spheres had the highest
magnification. Leeuwenhoek kept his
discovery secret, allowing others to
believe he was laboriously grinding
each tiny lens by hand.
During his lifetime, Van Leeuwenhoek
ground more than 500 optical lenses
and created more than 400 different
types of microscopes, of which nine
still exist. He made them from silver or
copper frames that held hand-ground
lenses.
Van Leeuwenhoek’s original specimens
can be found in the collections of the
Royal Society of London. His main
discoveries include infusoria (protists)
in 1674, bacteria in 1676, spermatozoa
in 1677, and the banded pattern of
muscular fibers in 1682.
SOURCES: The Handy Science Answer Book by the Science
and Technology Department of the Carnagie Library of
Pittsburgh; World Book Encyclopedia
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