Perhaps one of the biggest ironies in biology is that microbes, which are the oldest self-replicating organisms on Earth, were among the last to be discovered and have largely been ignored. The history of their discovery is, like many in science, based on the invention of new technologies. In this case, it was a microscope created by a man named Anton van Leeuwenhoek. But before the Dutchman could make his serendipitous yet groundbreaking discovery in the late 17th century, lens-making technology had to turn several corners and see some other significant findings first.
In the 14th century, crude lenses were being fabricated in Europe for correcting vision. Toward the end of the 16th century, the Dutch began to use Venetian glass, the clearest and the highest quality glass available, to fashion relatively high-quality lenses.
Early in the 17th century, two Dutch lens-makers fashioned a telescope by pairing a concave and a convex lens in a tube. Although the instrument was not much more than a crude spyglass, having a magnification of about seven- or eightfold, it was a huge breakthrough in technology at the time.
In 1609, Galileo Galilei, using a telescope made in Italy from a Dutch lens-maker’s design, observed that the moons of Jupiter orbited that planet rather than the Earth. Although Galileo’s instrument had a magnification of only about twentyfold, it was sufficient to allow him to zoom in on what we already could see with our naked eyes: planets, stars and the moon. His observations threatened the prevailing Ptolemaic, or geocentric, understanding of the solar system and changed the way we think about our planet, ourselves and our special relationship to the universe.
Although stories of Galileo and his telescope abound, a somewhat lesser-known fact is that he also developed a microscope around 1619. It was simply an inadvertent outgrowth of the invention of the telescope, since it had been known for several years that by inverting a telescope with two lenses, one could magnify objects nearby. So, the optical design of the telescope was inverted and put into a new housing.
The microscope was smaller than its counterpart, and the two lenses were set in a barrel made of leather and wood. Regardless, Galileo did not seem to have much interest in what he saw with his inverted telescope. He appears to have made little attempt to understand, let alone interpret, the smallest objects he could observe. In fact, it was so irrelevant to him that he didn’t even give it a name. It wasn’t until 1625 that his peers decided to call it microscopio.
A Closer Look
The difference between the telescope and the microscope is not simply the configuration of lenses; it is also in human perception and the anticipation of what is seen. While the lack of perception may be partially due to hubris, I think most often it is the lack of looking for patterns in nature in places that are not normally accessible to our limited senses. We can see objects far away with our naked eyes. Comets, meteorites, planets, moons, stars and even exploding stars can be seen without a telescope, and hence, when they are brought closer for inspection with such an instrument as the telescope, these distant objects are not so mysterious, just somewhat so. However, our eyes cannot see something much less than the width of a hair (about a tenth of a millimeter) without the aid of a magnifying device. On the scale of microscopic structures, we are virtually blind. If we can’t even understand that there is a microbial world, why would we look for it?
The discovery of the microbial realm, like so many findings in science, was an accident that changed the world as profoundly as Galileo’s observations. It required a focusing of the mind as much as of an instrument. The breakthrough came in 1665, when the English Royal Society published the first popular science book, Micrographia (with the subtitle Or Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses With Observations and Inquiries Thereupon). It was written by Robert Hooke, then a 30-year-old hunchbacked, cantankerous, neurotic hypochondriac who was also a brilliant natural scientist, polymath and an original fellow of the society that published the book.
Micrographia captured many people’s imaginations. In it, along with dozens of beautiful engravings based on meticulous illustrations by the author, Hooke provided not only a clear description of the architecture of fleas, the seeds of thyme, the eyes of ants, the internal makings of sponges, microscopic fungi and the small building blocks of plants, but he also provided a detailed description of his own microscope.
Hooke’s observations were based on a relatively simple compound microscope that had two lenses. Instrument-makers at the time were familiar with telescopes and designed microscopes with two lenses, very similar to that of Galileo’s. But two-lensed microscopes had a big, unanticipated problem that telescopes did not. In such simple compound microscopes, the first lens created a halo of many colors that the second lens magnified. The result was that the more one magnified the object, the more distorted the image became.
The microscope Hooke used was well made by the standards of the time, but the optics were still poor. It suffered from the large optical aberration that lens-makers could not avoid. The best instrument, regardless of how lovingly the fabricator decorated it, could magnify an object only by about twentyfold before it became almost worthless. Even at such low magnification, the images were fuzzy, and sometimes a bit of imagination was required to reconstruct the structure of the object in view. Regardless, Hooke’s skillful illustrations were mind-boggling at the time, and the publication of Micrographia sparked interest in the construction of better lenses.