Nerdy Science Blog

Our modern world is built around tiny things, things much too small for the unaided eye to puzzle out - microscopic things, in fact. And much of what we know about those tiny things has been discovered with microscopes. Many great men throughout history have made their famous discoveries while staring through the eyepiece of a microscope. We owe the microscope a huge debt - but where did it come from?

Before the microscope, there was the magnifying glass. Roger Bacon is often credited with the invention of the magnifying glass, although his work was built on foundations laid by Arab scientists. It had been known from ancient times (as early as ~200 C.E.) that convex, transparent materials could concentrate light in such a way as to set fire to flammable materials, but Bacon’s work made the convex lens useful for visual exploration of the world of small things. Magnifying glasses were combined with hollow tubes that had a flat platform for the object to be examined, with a single lens at the opposite end and used to examine fleas and other very small objects. These came to be known as “flea glasses”.

Towards the end of the 16th Century, during the Renaissance, Zaccharias Janssen and his son Hans were experimenting with multiple lenses in tubes, and discovered that these combinations could produce significant magnification of nearby objects. This discovery appears to have been the foundational research that produced both the telescope and the microscope. It was just a few years later, about 1620, when Galileo heard of this and worked out the principles that allowed him to build a telescope with a focusing system.

During the 17th century, a man named Anton van Leeuwenhoek became fascinated with small things and magnification. Leeuwenhoek was an extremely unlikely scientist, holding no university degree or advanced education and being born of tradesmen. Fortunately for the future, he was diligent, careful, skillful and curious. This led him to begin to grind and polish extremely precise, tiny lenses with great curvature. These lenses eventually produced a magnification of 270 diameters, an accomplishment unmatched at the time. He went on to discover bacteria, blood cells, sperm cells, nematodes, and many other tiny objects. His research was directly responsible for bringing the microscopic to the attention of the scientific community of the time, through more than a hundred carefully written letters to the French Academy and the Royal Society of England. He is believed to have made over 500 microscopes, but fewer than ten remain today.

Leeuwenhoek’s microscopes used a single optical element, and this limited their magnification. Over the next hundred years or so there were incremental improvements in lensmaking that made the microscope easier to use and view. The next major breakthrough was demonstrated by Joseph Jackson Lister in about 1830, who showed that multiple lenses with much less curvature could be assembled in such a way as to reduce spherical and chromatic aberration, and development of the compound microscope began in earnest. Some of the best microscopes of the time were made in America by Charles A. Spencer who developed a reputation for building the best instruments money could buy. He’s widely believed to be America’s first microscope manufacturer.

Zeiss Optical Works Director Ernst Abbe developed a mathematical formula that allowed the calculation of the maximum possible magnification that an optical microscope could produce. He called it the Abbe Sine Condition. The microscopes that Abbe and Zeiss produced based on Abbe’s calculations were the first ever built on a sound mathematical understanding of the optics of microscopy lenses. When Abbe and Zeiss partnered with Otto Schott and developed new methods of eliminating optical flaws from the glass they were making lenses from, the apochromat was born. This optical advancement essentially eliminated chromatic aberration and brought optical microscope resolution to the theoretical limits of the resolution of visible light, which breaks down at about half a micron. No amount of glass design or precision in manufacturing will improve on this limit; a new technology was needed.

This new technology came in 1931 with the invention of the electron microscope, developed by two German engineers, Ernst Ruska and Max Knoll. This device accelerated electrons until their wavelength was a hundredth of that of visible light, allowing resolution of objects down to the atomic level. This was a Transmission Electron Microscope - followed before too long by the development of the Scanning Electron Microscope, by Max Knoll in the mid 1930s, and further developed by Manfred Von Arden, then by Sir Charles Oatley and Gary Stewart. This device and process has produced many of the images we’ve become accustomed to seeing - the monochromatic images of diatoms and the heads of ants that reveal the slightest textural variation and incredible detail.

Development continues as we try and find better ways of visualizing the world of tiny things. We’ve seen bacteria, chromosomes, molecules, crystalline lattices, and the eyes of tiny insects, and become accustomed to the apparently casual ease with which we view incredibly small objects. It’s important to remember that there’s a long and interesting history behind each of our technologies today, and the microscope is certainly no exception.

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