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A History of the Microscope

In delving into a history of the microscope, we must begin in the time of pre-history, before written records were made. Humans are curious creatures, and it is assumed that someone found a clear rock or crystal that was relatively smooth, but wider in the middle than on the edges. This crystal would have made objects behind it look larger. Not only this, when the sun's rays came through it, the object upon which it was directed would be heated to the point of catching fire. Later in Rome, where practical things were appreciated, these magnifying rocks were noted in the writings of Seneca and as cauterizing crystals by Pliny the Elder.

Although they were used for limited magnification in some crafts, such crystals were relatively rare and thus not widely used. It was also known by ancients that water in a clear receptacle could magnify, but the distortion of the image and the expense often made common use impractical. However, about the end of the 1200s, glass making techniques coupled with advances in understanding in optics allowed for the invention of eye-glasses or spectacles from the lens (called lens because of its similarity in appearance to a lentil1).

Flea Glasses

The next step toward the microscope was taken in the 1500s by the development of a small tube fitted with two pieces of glass such that the part nearer the eye was convex and the other terminated in a flat piece of glass. This device was commonly used to closely examine small creatures such as the flea. Thus, the "flea glass" came into common use. Nevertheless, it was thought of more as a parlor device for entertainment than it was as an instrument for the advancement of scientific study.

The Dutch Influence

One van Leeuwenhoek Microscope

Some Dutch spectacle makers saw the possibilities of getting even greater magnification from this arrangement. Zaccharias and Hans Janssen (in the 1590s) created early devices for magnifying objects close up and at a distance by using two convex lenses. Their microscope is now called a "compound microscope". But it was Anton van Leeuwenhoek (even though his microscope had only a single lens) who finally put the microscope to practical and scientific uses. His own invention was based on the magnifying glasses that were used to count threads in textiles (to measure the quality of weaved material in dry-good stores). He created his own tiny lenses with extreme curvature that could magnify objects as much as 270 times. These, he placed into a thin board which was connected by bolts and brackets to a needle which held the specimen. The bolts could be turned to adjust the distance the specimen was held from the aperture for better, more focussed viewing. (See illustration.)

Van Leeuwenhoek became the father of microscopy for the detailed observations he made using the device, as well as the experiments he conducted. Students of entomology, studying insects, would use his style of microscope for several centuries. He gained renown for studying the flow of blood in capillaries, microscopic organisms in water, and yeast. He reported his findings to the Royal Society of England and the French Academy.

Robert Hooke

Old Microscope

Another pioneer in the use of the microscope was Robert Hooke an Englishman and member of the Royal Society at about the same time as Sir Isaac Newton. He published a book called Micrographia, which among other things, contained drawings of over 100 specimens, and described the use and benefits of the microscope. Hooke helped people to take seriously a device that was, at the time, thought to be about as useful as a kaleidescope.

Advancement in Microscopes Accelerates

As demand from investigators, scientists, naturalists, and university researchers increased, advancements in the development of the microscope quickened. Ingenious mechanisms were built to adjust focus by moving lenses, direct light via mirrors, and stabilize the platform. Better and better optics and lenses made possible magnifications that could hardly have been conceived in ancient times, revealing a world that few had suspected, and fewer still had imagined. A compound, light microscope can magnify an object 2000 times with normal light and up to 5000 times with a blue light. (Although new techniques by such scientists as Hess and Betzig are expanding the magnification even further.2)

But as is common in human exploration, the avid scientist wished to go further still into the unknown world of the small. The light microscope, no matter how many lenses it uses can only magnify so far. Its limitations are based on the wavelength of light. At a certain point objects become so small that they do not reflect or distort light enough to create an image for the naked eye. This point is .275 micrometers or about 1/100,000ths of an inch. But there are rays with wavelengths shorter than light. The trick is catching them and turning them into something that the eye can see.

Development of the Electron Microscope

In 1931 the idea for the electron microscope was hit upon. Two Germans, Ernst Ruska and Max Knott shot electrons at a very high speed in a vacuum through a aperture at a wavelength 100,000 times smaller than that of light. By this time the art of photography had been invented, and the shot of electrons went through the specimen and onto a photographic plate that was sensitive to them. The image that was left behind was that of the specimen. Using this method even individual atoms and molecules can be seen. This is a magnification of a million times. The limitation of this device though, is that the specimen must also be in the vacuum. In this position, most living creatures cannot survive and will not act normally. Thus, most of the images received are still and unmoving.

Today, the light microscope is still in common use especially in the life-sciences where it is quite useful in observing biological processes. New uses of video, stains, dyes, and other techniques are constantly being tried to enhance the value of this instrument. Electron microscopes are far more expensive to use, so they are more common in studies with large budgets and that require very great magnifications. Quality light microscopes are readily available, and are common in schools, and even the homes of those with a yen for investigation and learning.

Next Page: Compound Light Microscopes (Bright Field)

1. On-line Etymology Dictionary on the Word Lens

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