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Chapter 1.
Early History of the Lens:
The first use of a lens is a bit of a mystery, but it's now believed that use of
lenses is more modern than previously thought.
This chapter should give some insighs on how optical theory developed making
microscopy possible.
The Lanyard Lens:
The above is the famous "Lanyard Lens" discovered at Nimrod by
Lanyard, and datable to 721-705 BC. This was long thought to be the first
example of a plano-convex lens. In the last century, however, studies of this
object have shown that the curved surface is actually faceted, and not rounded,
as one would have done to make a lens. Secondly, cloudy striae within the stone,
which add an aesthetic quality, make it a poor magnifier. It is now generally
agreed that this stone was actually just an ornament which fell away from it's
mounting. It's now thought that lenses were not used nearly so long ago.
Ancient Writings of Optics
Several ancient manuscripts give us datable evidence of the state of refraction
and optics throughout the ages.
- 2nd Century BC: Claudius Ptolemy:Described a stick
appearing to bend in a pool of water, and accurately recorded the angles to
within 1/2 degree for this relationship. He then very accurately calculated
the refraction constant of water.
- 1st Century AD: Seneca: Described actual magnification by
a globe of water. He wrote the following: "Letters, however small
and indistinct, are seen enlarged and more clearly through a globe of glass
filled with water."
- 962-1038 AD: Arabian Scholar Alhazen: Wrote the first
major optical work Opticae Thesaurus discussing not only optical
principles, but described the anatomy of the eye, and how the lens of the
eye focuses an image on the retina.
- 1267 AD Bacon Wrote definite descriptions of simple
magnification in his Perspectiva of 1267: "Great things can
be performed by refracted vision. If the letters of a book, or any minute
object, be viewed through a lesser segment of a sphere of glass or crystal,
whose plane is laid upon them, they will appear far better and larger.
While the above exerpts give a glimpse at optical knowledge in the past, it's
important to realize that this knowledge was likely confined to the learned
scientists and philosophers. It wasn't until the invention of spectacles that
optics came into common use.
Early Evidence of Spectacle Use:
It has been said that spectacles were in use in China well before they were
known in the West. However, studies of early Chinese spectacles show that often
the lenses were planar, without corrective abilities, and people may have
actually used these colored glasses for cosmetic purposes rather than for
astigmatism.
There is one very early description of an isolated use of spectacles. Pliny
the Elder wrote the following in 23-79 A.D.:
"Emeralds are usually concave so that they may concentrate the visual
rays. The Emperor Nero used to watch in an Emerald the gladatorial
combats."
This quote appears to be the first description of using a monacle for correcting
short-sighted vision. Strangely, even though this must have worked quite well,
and many people must have read this passage, there is no other evidence of
spectacle use for over twelve centuries.
The Invention of Spectacles:
The modern reinvention of spectacles occurred around 1280-1285 in Florence,
Italy. While it's uncertain who the inventor was, it is quite clear that
spectacles quickly took hold into common use in that city, and use of them
spread outward to the rest of the known world in just a few years. Considering
the large percentage of people with visual problems, it's not difficult to
understand why there was such enthusiasm.
Strangely, it's not certain who in Florence made the first spectacles. Some
give credit to a nobleman named Amati who died in 1317. It has been said that he
made the invention, but told only a few of his closest friends.
The First Compound Microscope:
The story of the first "compound" (more than 1 lens) microscope is an
interesting one. Much is unknown, yet many things are known.
With the lenses of spectacles widespread, and their obvious magnification
properties, it was only a matter of time before someone put two together to make
the first compound microscope. Indeed, this was probably already happening with
telescopes just before this as Dutch Spectacle makers were experimenting with
multiple lenses. Since a microscope could be made by just reversing a telescope,
this may be where the idea originated.
There is a terrific amount of mis-information about who invented the
microscope. Fairly respectable references have said Gallileo invented it shortly
after inventing the telescope. This is not so, as Gallileo didn't purchase his
first telescope until around 1607. Many people think that Leeuwenhoek invented
the microscope. This is also very untrue, as while his microscopes were very
simple and crude, he started making them long after very elaborate models were
available and many important discoveries had been made by them.
 Zacharias Jansen
Credit for the first microscope is usually given to Zacharias Jansen, pictured
above, in Middleburg, Holland, around the year 1595. Since Zacharias was very
young at that time, it's possible that his father Hans made the first one, but
young Zach took over the production.
Details about these first Jansen microscopes are not clear, but there is some
evidence which allows us to make some good guesses about them. The below early
microscope found in Middleburg, Holland, corresponds to our expectations of the
Jansen microscopes.
 Early
Microscope Attributed to Jansen
Unfortunately, no early Jansen microscope has survived to the present. The above
instrument surfaced in Middleburg, Holland, in the 17th century, and was
reported to be an early Jansen made microscope. That microscope now resides in a
Middleburg museum. Most historians have come to doubt the origin of the above
microscope, but because it corresponds well with the known description of the
Royal Jansen microscopes, it is at least very similar to the Jansen microscopes.
The Royal Jansen Microscopes
Luckily, there was one true Jansen microscope which survived long enough to be
studied. As was customary at the time, the Jansens made several versions of
their new invention to give to royalty. We know that they sent one of their
microscopes to Prince Maurice of Orange, and one to Archduke Albert of Austria.
While neither of these instruments survived to modern times, the later of them
was preserved until the early 1600's, when a Dutch diplomat and childhood friend
of Zacharias Jansen named Cornelius Drebbel, examined it and recorded his
observations.
We would expect a royal presentation microscope to be more ornate and
well-made than usual, yet it should retain the same mechanical configuration.
Drebbel described the royal instrument as being composed of 3 sliding tubes,
measuring 18 inches long when fully extended, and two inches in diameter. It was
very ornate, with 3 brass dolphins at the end, forming the feet of a tripod.
Besides the ornate tripod, this description is quite similar to the microscope
found in Holland.
 Optics of the Jansen-style
Microscope:
The above diagram shows the optics of the Jansen-style microscopes. Note that it
contains a 2 lenses, and diaphragms between the tubes to cut down on glare from
the crude lenses. The microscope at the Middleburg museum was said to have a
magnification of 3X when fully closed, and 9X when fully extended.
Probably the first major improvement in microscope optics was the
introduction of a 3-lens system. This happened early, possibly by Robert Hooke
(described later), by using a 2-lens "Huygens" eye-piece which was in
common use on telescopes.
The Rapid Spread of Knowledge:
After the Jansen invention, word traveled rapidly throughout the known world.
Within just a few years, there were many microscope makers throughout europe,
and learned men such as Galileo were using them.
Microscopes of the 17th Century:
The seventeenth century was a period of great interest in microscope, as well as
some of the earliest discoveries. The word "Microscope" was
first coined by members of the first "Academia dei Lincei" a
scientific society wich included Galieleo. But the microscope wasn't just a
scientific tool. Throughout this century and Victorian times, microscopes were
owned by the upper-class as recreational toys.
Three Lens System
As mentioned before, the first technical advancement of the Microscope after
Jansen was revision of it's optics from the 2-lens system to the 3-lens system,
early in the century. In the above diagram, B is the eye-lens, D is the Field
lens, and F is the objective lens. The eye views at point A. It has been said
that Robert Hooke was the first to use this, by using the 2-lens "Huygens"
eyepiece which was standard for the telescope. This allows for better
conservation of light from the object, while avoiding a very large eye-lens from
which the eye must be held an uncomfortable distance away. This three-lens
system remains the standard configuration of microscopes today, except that that
each lens may be made out of a combination of close lenses.
Why the Utility of Microscopes was Questionable:
In the early 17th century, a few papers were published on microscopic findings,
but the first two important papers weren't until 1660 and 1665, when Marcello
Malpighi proved William Harvey's blood circulation theories, and Robert Hooke's
wrote his "Micrographia."
The significance of these works may be difficult to understand today. It
wasn't clear back then that the microscope would ever be useful to make
scientific discoveries. Some thought that although it was interesting to look at
the tiny legs on a flea or parts of other insects, you couldn't really make any
new discoveries with such a device. It wasn't appreciated that by looking at
things up close, you would be able to see anything really different than at a
distance. This thought can be understood by considering examination of
"milk" under a microscope: nothing really new becomes visible -- there
just isn't any structure which becomes apparent at the magnification involved.
These early thinkers had no idea that a very important structure lies in all
living tissues that was within the reach of light microscopes: The Cells.
 Marcello Malpighi, circa 1660
Marcello Malpighi was one of the first great microscopists, and even today is
considered the father of embryology and early histology. His first discovery
with the microscope was of monumental importance in animal physiology.
Just 21 years earlier, William Harvey stunned the academic and medical
environment in the publication of his "De motu cordis & sanguinis in
animalibus" in which he presented experimental and logical proof that
the long-held theories of Galen were wrong, and that blood actually travels in a
circular motion from the heart, around the body, then back to the heart. [Since
the time of Galen, it was thought that the blood is produced from the
intestines, travels to the liver, then the heart, and then is distributed to the
body by both veins and arteries, where it is consumed.] In this time such a
radical idea should have been met with banishment, yet Harvey's important
position as a top physician to royalty, as well as his meticulous theoretical
and logical proof, made the world stop to consider it. But, as convincing as his
argument and evidence was, his theory required some form of connection between
the arteries and the veins, which nobody could see.
In 1660, 3 years after Harvey's death, Marcello Malpighi used a microscope to
see the capillaries, the microscopically thin blood vessels which formed the
needed connection between the arteries and veins.
For the next 200 years, "Fish-Plates" (brass curved plates with
which one would tie down a small fish) became standard equipment for
microscopes. This allowed viewing of corpustels (red blood cells) traveling
through the transparent tail capillaries. This interest illustrates the
importance of the capillary discovery.
 17th Cent. Italian Models as
Malpighi Likely Used:
The above two microscopes are of the type made in Italy, around the time
Malpighi did his work. These are small hand-held items, maybe 5-8 inches tall -
quite a contrast to the 2-foot tall instruments being made in England around the
same period. The left-most item was made by Giuseppe Campani (1635-1715) and the
right-most item was made by Eustachio Divini (1610-85.) A great deal has been
written on Malpighi's life, and it is not completely certain which microscopes
he used, but his personal papers do mention purchase of a Divini microscope, and
the item on the right is often considered to be the type used by him.
 Italian Microscope as Galileo May have used.
The above microscope is another simple Italian style from the early 1600's,
which is said to be the type Galileo used. It is interesting to note that
Italian microscopes remained of this smaller, simpler type for some time, while
the English microscope makers were rapidly making two foot tall monsters with
many mechanical innovations.
 Robert Hooke's Micrographia, 1665
Robert Hooke was a mechanical genius who graduated from Oxford, and worked with
Robert Boyle in his famous gas experiments. Robert Hooke's Micrographia
was an important milestone in proving the importance of microscopy. The
following image of cork is probably the classic example of Hooke's
accomplishments.
 Hooke's Drawing of Cork.
Before Hooke's time, it wasn't known why cork had the unusual properties that it
had: it was very light, and could float well on water, and it was firm, yet
could compress under force. When Hooke looked at a thin slice of cork under the
microscope, it became clear why cork had these properties. He could see that the
substance was mostly air, with pieces of material making up a mesh-work of
supporting structure around the tiny air pockets. Hooke named these pockets of
air "cells" after the small monastery rooms they reminded him off.
While he didn't at the time understand that these air "cells" were the
shadow remains of what is now considered a cell, the name remains.
 Hooke's Microscope by Cock, 1665
The microscope used by Hooke was illustrated in his paper. Hooke did not make
his own microscopes; they were made by London instrument maker Christopher Cock,
whom Hooke gave much advice on design. In return, the success of Hooke's book
made Cock a very famous microscope maker, and popularized the side-pillar
design.
These were large instruments, sometimes nearly 2 feet tall. The very large
body tube was attached to the stand by a screw, so by rotation, an object could
be brought into focus. The object was placed on a pin on the lower stage, and
light illuminated the object from above. The shown illumination apparatus, an
oil flame and a globe and lens to focus the light, has been said to be made by
Hooke himself.
Obviously with the weight of a 2 foot tall body tube, and the crude screw
threads that were possible at the time, there was a great deal of wobble
associated with screwing the focus up and down. Later models made by Christopher
Cock had a much wider nose to increase stability. Below is slightly later
version, again made by Cock, which has a wider nose screw.
Another Microscope by Cock, after 1665.
Several other examples exist in such collections as "The Billings
Microscope Collection" and the "Royal Microscope Society
Collection." These are usually very beautiful instruments, using bright and
ornate tooling along the leather tube covers, brass uprights, and Lignum Vitae,
a very hard black wood.
John Yarwell and the English Tripods
Later in the 17th century, microscopes made a morphological change. Probably due
to the instability of the thin side-pillar and small screw-nose holding the huge
tube on the Cock/Hooke style of microscope, the English Tripod became popular.
 Tripod Sketched an 1631 Journal
The earliest evidence of an english tripod style microscope was from the Journal
of a Dutch schoolmaster, Isaac Beeckman, who draw the above in his diary in
1631.
 Tripod in Yarwell's 1683 Trade Card.
John Yarwell, who was probably the next great microscope maker, showed the above
microscope in his trade card of 1683. It is similar in size, body tube, and
focus to the side-pillar model of Cock, and the object lies flat on a small
platform. The improvement was the more sturdy tripod holding the large tube
straight up and down.
Another 17th Century Tripod, 1680's
Many English-Tripod-Style microscopes were made in the 1680's, but very few
exist today, confined mostly to museums. The above is a fine example.
Leeuwenhoek and the Use of Simple Microscopes:
Antoni van Leeuwenhoek (circa 1670)
In the later part of the 17th century, something quite unexpected happened in
microscopy. Using tiny single-lens microscopes of his own design, this Dutch
Draper/amateur scientist, started making incredible discoveries. He began
writing letters to the Royal Society in London in 1673, which were published in Philosophical
Transactions. He described experiments which could be performed with simple
microscopes, and made exciting drawings of his microscopic world. Leeuwenhoek
make the first descriptions of protozoa, bacteria, and spermatozoa which he
called "animalicules" and made the first detailed descriptions of the
red blood cell.
It would seem incredible that an amateur could out-do the scientific
community using simple instruments of his own making, but the reasons
Leeuwenhoek was successful are simple. The lenses in common use in the 17th
century were quite crude, often made by smashing molten glass between pieces of
wood. Because of optical problems such as chromatic and spherical aberration
(described later) the images at modest magnifications (over 40 or 50X) were
blurry, with colorful halos. When multiple lenses are used, this error is
synergistically increased. By using only a single, high-power, quality lens,
Leeuwenhoek found he could get much clearer images than with compound
microscopes.
A recent study of the remaining Leeuwenhoek microscopes shows their
magnifications to be from 50X over 200X, with resolutions as good as 2 microns.
Until around 1800, the compound microscopes could only resolve as well as around
5 microns.
 A Leeuwenhoek Microscope
This diagram shows a microscope by Leeuwenhoek. It is about 3-4 inches high, and
made of two brass plates riveted together. A small hole is made in the plates,
between which the very tiny but high-power lens is placed. On the back side, a
screw with a needle provides a place to place the object, and allows crude
focusing.
How a Leeuwenhoek Microscope is Used:
This photo shows how a Leeuwenhoek microscope is used. After attachment of the
object, the entire microscope must be held very close to the eye. This is not
easy to do, as the faint image is hard on the eyes, and focus of the crude
device requires great patience. But for the price of convenience, the images
obtainable were greatly superior to the compound microscopes. Robert Hooke,
author of the early Micrographia, said in his Microscopium lecture of
1679:
I have found the use of them [simple microscopes] offensive to my eye, and to
have much strained and weakened the sight, which was the reason why I omitted
to make use of them though in truth they do make the object more clear and
distinct, and magnify as much as the double [compound] microscopes; nay, to
those whose eyes can well endure it, it is possible with the single microscope
to make discoveries much better than with a double one, because the colours
which do much disturb the clear vision in double microscopes is clearly
avoided and prevented in the single.
Leeuwenhoek's Secret Lenses:
Leeuwenhoek's method of making the tiny, high-quality and high power lenses was
kept secret. A study has recently been done on the few remaining copies of
Leeuwenhoek's microscopes, and it appears that some of the lenses may have been
made by grinding, while the best ones were blown. Leeuwenhoek learned that when
a glass bulb is blown, a small drop of thickened glass forms at the bottom of
the bulb (much like a drop sits in the bottom of a blown soap bubble.) By
carefully breaking away the excess glass, this tiny drop can be used as a lens.
The Mystery of the Leeuwenhoek Microscopes:
In 1747, two years after Leeuwenhoek's death, over 500 of these small
microscopes were auctioned off, and 26 special silver microscopes were given to
the Royal Society of London. Of this very large number, only nine microscopes
are known to exist today. Even the 26 silver instruments which became part of a
large and famous collection somehow disappeared. The nine Leeuwenhoek
Microscopes are priceless -- often they are kept in a museum safe and only a
replica is on display for the public. As the years go on, it becomes less likely
that another specimen will turn up, but forgeries have turned up and will likely
continue to surface.
The Simple Microscope Remains Important:
After Leeuwenhoek's incredible successes, simple microscopes regained their
place as complements to compound microscopes. In fact, up until the early 19th
century, some of the best microscopes could be used both as simple or compound
microscopes. When George Adams made a presentation microscope for King George
III at the end of the 18th century, it was actually two complete microscopes
attached back to back: a simple microscope, and a compound microscope.
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