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 During that historic period known as the Renaissance,
after the "dark" Middle Ages, there occurred the
inventions of printing, gunpowder and the mariner's
compass, followed by the discovery of America.
Equally remarkable was the invention of the light
microscope: an instrument that enables the human
eye, by means of a lens or combinations of lenses, to
observe enlarged images of tiny objects. It made visible
the fascinating details of worlds within worlds.
The definition of a
microscope: An
instrument for
viewing objects that
are too small to be
seen easily by the
naked eye.
Invention of Glass Lenses
Long before, in the hazy
unrecorded past, someone picked
up a piece of transparent crystal
thicker in the middle than at the
edges, looked through it, and
discovered that it made things look
larger.
 Someone also found that such a crystal would focus
the sun's rays and set fire to a piece of parchment or
cloth. Magnifiers and "burning glasses" or "magnifying
glasses" are mentioned in the writings of Seneca and
Pliny the Elder, Roman philosophers during the first
century A. D., but apparently they were not used much
until the invention of spectacles, toward the end of the
13th century. They were named lenses because they are
shaped like the seeds of a lentil.
Circa 1000AD – The first vision aid
was invented (inventor unknown)
called a reading stone. It was a glass
sphere that magnified when laid on
top of reading materials.
Circa 1284 - Italian, Salvino
D'Armate is credited with
inventing the first wearable eye
glasses.
 1590 – Two Dutch eye glass makers,
Zaccharias Janssen and son Hans
Janssen experimented with
multiple lenses placed in a tube.
The Janssens observed that viewed
objects in front of the tube
appeared greatly enlarged, creating
both the forerunner of the
compound microscope and the
telescope.
 Birth of the Light Microscope
 About 1590, two Dutch spectacle makers, Zaccharias
Janssen and his son Hans, while experimenting with
several lenses in a tube, discovered that nearby objects
appeared greatly enlarged. That was the forerunner of
the compound microscope and of the telescope. In
1609, Galileo, father of modern physics and astronomy,
heard of these early experiments, worked out the
principles of lenses, and made a much better
instrument with a focusing device.
 The earliest simple microscope was merely a tube with
a plate for the object at one end and, at the other, a
lens which gave a magnification less than ten
diameters -- ten times the actual size. These excited
general wonder when used to view fleas or tiny
creeping things and so were dubbed "flea glasses."
Types of scopes
 Microscopes are used both in classrooms and in
making important evaluations in medical laboratories
and other microtechnologies. The different types of
microscopes are designed for these different uses, and
therefore will vary based on their resolution,
magnification, depth of field, field of view,
illumination method, degree of automation, and type
of image they produce. There are essentially three
categories of microscopes: electron, confocal, and
compound.
1665 – English physicist, Robert
Hooke looked at a sliver of cork
through a microscope lens and
noticed some "pores" or "cells" in it.
1674 – Anton van Leeuwenhoek
built a simple microscope with only
one lens to examine blood, yeast,
insects and many other tiny
objects.
Leeuwenhoek was the first person
to describe tiny cells and bacteria
invented and he invented new
methods for grinding and polishing
microscope lenses that allowed for
curvatures providing
magnifications of up to 270
diameters, the best available lenses
at that time.
 Robert Hooke
 Robert Hooke, the English father of microscopy, re-
confirmed Anton van Leeuwenhoek's discoveries of
the existence of tiny living organisms in a drop of
water. Hooke made a copy of Leeuwenhoek's light
microscope and then improved upon his design.
 Anton van Leeuwenhoek (1632-1723)
 The father of microscopy, Anton van Leeuwenhoek of
Holland, started as an apprentice in a dry goods store
where magnifying glasses were used to count the threads in
cloth. He taught himself new methods for grinding and
polishing tiny lenses of great curvature which gave
magnifications up to 270 diameters, the finest known at
that time. These led to the building of his microscopes and
the biological discoveries for which he is famous. He was
the first to see and describe bacteria, yeast plants, the
teeming life in a drop of water, and the circulation of blood
corpuscles in capillaries. During a long life he used his
lenses to make pioneer studies on an extraordinary variety
of things, both living and non living, and reported his
findings in over a hundred letters to the Royal Society of
England and the French Academy.
 18th century – Technical
innovations improved microscopes,
leading to microscopy becoming
popular among scientists. Lenses
combining two types of glass
reduced the "chromatic effect" the
disturbing halos resulting from
differences in refraction of light.
 Compound microscopes are mostly used in biology.
They give a 2-D slice of an object, yet can attain a high
enough magnification to see parts of eukaryotic cells, a
hair strand, or pond scum. Unfortunately, they do not
have excellent resolution, so the image may be blurry.
On the other hand, stereoscopic microscopes, as the
name implies, provide a 3-D picture of bisected items,
like muscle tissue or an organ. In this case,
magnification is poor, so you can't make out separate
cells, but resolution is much improved.
 Finally, there are the simplest types of microscopes
found in classrooms across the world: compound
microscopes. These are entirely operated by hand and
use the ordinary ambient light from the sun or a light
bulb to illuminate the specimen. Whatever you want
to look at is mounted between two glass slides and
clipped beneath the main lens. You use a dial to focus
the image. These tools use a simple series of
magnifying lenses and mirrors to bring the image up
to an eyepiece, much like a telescope.
 1830 – Joseph Jackson Lister
reduces spherical aberration or the
"chromatic effect" by showing that
several weak lenses used together
at certain distances gave good
magnification without blurring the
image. This was the prototype for
the compound microscope.
 Beyond the Light Microscope
 A light microscope, even one with perfect lenses and
perfect illumination, simply cannot be used to distinguish
objects that are smaller than half the wavelength of light.
White light has an average wavelength of 0.55 micrometers,
half of which is 0.275 micrometers. (One micrometer is a
thousandth of a millimeter, and there are about 25,000
micrometers to an inch. Micrometers are also called
microns.) Any two lines that are closer together than 0.275
micrometers will be seen as a single line, and any object
with a diameter smaller than 0.275 micrometers will be
invisible or, at best, show up as a blur. To see tiny particles
under a microscope, scientists must bypass light altogether
and use a different sort of "illumination," one with a shorter
wavelength.
 1872 – Ernst Abbe then research
director of the Zeiss Optical Works,
wrote a mathematical formula called
the "Abbe Sine Condition". His formula
provided calculations that allowed for
the maximum resolution in
microscopes possible.
 Your scope has an Abbe condenser
1903 – Richard Zsigmondy
developed the
ultramicroscope that could
study objects below the
wavelength of light. He won
the Nobel Prize in Chemistry
in 1925.
1932 – Frits Zernike invented
the phase-contrast
microscope that allowed for
the study of colorless and
transparent biological
materials for which he won
the Nobel Prize in Physics in
1953.
 A confocal microscope is a step down from the
previous types. It uses a laser beam to illuminate a
specimen whose image is then digitally enhanced for
viewing on a computer monitor. The specimen is often
dyed a bright color so the laser gives a more
contrasting image. It is mounted on a glass slide just
like in high school biology. Confocal microscopes are
controlled automatically, and motorized mirrors help
with auto-focus.
 1931 – Ernst Ruska co-invented the electron
microscope for which he won the Nobel Prize in
Physics in 1986. An electron microscope depends on
electrons rather than light to view an object, electrons
are speeded up in a vacuum until their wavelength is
extremely short, only one hundred-thousandth that of
white light. Electron microscopes make it possible to
view objects as small as the diameter of an atom.
 1981 – Gerd Binnig and Heinrich
Rohrer invented the scanning
tunneling microscope that gives
three-dimensional images of
objects down to the atomic level.
Binnig and Rohrer won the Nobel
Prize in Physics in 1986. The
powerful scanning tunneling
microscope is the strongest
microscope to date.
 Electron microscopes are extremely sophisticated
types of magnification devices. These are used in
archaeology, medicine, and geology to look at surfaces
and layers of objecs such as organs and rocks. Instead
of using light, these devices point a stream of electrons
at the specimen and attached computers analyze how
the electrons are scattered by the material. The
specimen must be suspended within a vacuum
chamber.
 With transmission electron microscopes, a scientist
gets a view of 2-D slices of the object at different
depths. Of course, with such powerful instruments,
both the degree of magnification and the resolution,
or sharpness of the image, are very high. Scanning
electron microscopes are slightly different in that they
scan a gold-plated specimen to give a 3-D view of the
surface of an object. This view is in black and white,
yet gives an amazing picture of, for example, the
minute hills and valleys of a dinosaur bone.
 Charles A. Spencer
 Later, few major improvements were made until the
middle of the 19th century. Then several European
countries began to manufacture fine optical
equipment but none finer than the marvelous
instruments built by the American, Charles A.
Spencer, and the industry he founded. Present day
instruments, changed but little, give magnifications up
to 1250 diameters with ordinary light and up to 5000
with blue light.
 Electron Microscope
 < Introduction: History of Early Light Microscopes
 The introduction of the electron microscope in the 1930's
filled the bill. Co-invented by Germans, Max Knott and
Ernst Ruska in 1931, Ernst Ruska was awarded half of the
Nobel Prize for Physics in 1986 for his invention. (The
other half of the Nobel Prize was divided between Heinrich
Rohrer and Gerd Binnig for the STM.)
 In this kind of microscope, electrons are speeded up in a
vacuum until their wavelength is extremely short, only one
hundred-thousandth that of white light
 Beams of these fast-moving electrons are focused on a cell
sample and are absorbed or scattered by the cell's parts so
as to form an image on an electron-sensitive photographic
plate.
 Power of the Electron Microscope
 If pushed to the limit, electron microscopes can
make it possible to view objects as small as the
diameter of an atom. Most electron microscopes
used to study biological material can "see" down to
about 10 angstroms--an incredible feat, for
although this does not make atoms visible, it does
allow researchers to distinguish individual
molecules of biological importance. In effect, it
can magnify objects up to 1 million times.
Nevertheless, all electron microscopes suffer from
a serious drawback. Since no living specimen can
survive under their high vacuum, they cannot
show the ever-changing movements that
characterize a living cell.
 Light Microscope Vs Electron Microscope
 Using an instrument the size of his palm, Anton van
Leeuwenhoek was able to study the movements of onecelled organisms. Modern descendants of van
Leeuwenhoek's light microscope can be over 6 feet tall, but
they continue to be indispensable to cell biologists
because, unlike electron microscopes, light microscopes
enable the user to see living cells in action. The primary
challenge for light microscopists since van Leeuwenhoek's
time has been to enhance the contrast between pale cells
and their paler surroundings so that cell structures and
movement can be seen more easily. To do this they have
devised ingenious strategies involving video cameras,
polarized light, digitizing computers, staining and other
techniques that are yielding vast improvements in contrast,
fueling a renaissance in light microscopy.