It was a time in which the Church held unbridled power, and of extensive witch hunts throughout Europe. According to the law of the time, mere suspicion was enough to prompt a witch trial. Thousands, mostly women, were tortured and executed. The persecution of witches, which was legal in Europe from the 15th to well into the 18th century, is one of the blackest chapters in the history of humanity.
The 17th century was also marked by outstanding personalities, such as the dramatist William Shakespeare, the painter Rembrandt, the philosopher Francis Bacon, the philosopher and mathematician René Descartes, the physicist and astronomer Galileo Galilei, the philosopher and mathematician Gottfried Leibniz, the composer Claudio Monteverdi, the physicist and mathematician Isaac Newton, the mathematician, physicist and astronomer Christiaan Huygens (inventor of the two-lens Huygens eyepiece), the astronomer Johannes Kepler, and the poet John Milton.
Woodcut from the "Praxis rerum criminalium iconibus illustrata", a Latin book on criminal law by Joost de Damhouder (1507–1581) of Antwerp, a legal expert renowned throughout Europe. The content was not new, as Damhouder had no reservations about plagiarizing the works of others. The virtue of honesty, which is so important for practitioners of the law, certainly did not apply to him. Nevertheless, the many woodcuts that vividly illustrate the various aspects of the judicial process were a revolutionary innovation. Unfortunately, his work influenced criminal law throughout Europe and served as the basis for a number of witch trials.
The idea of observing magnified images of objects through two glass lenses arranged in series first appeared in scientific writing in the early 16th century. It wasn't until the early 17th century, during the Baroque era, that the first optical instruments were built consisting of a series of lenses: the telescope (from the Greek tele, meaning distant, and skopein, to observe) and the microscope (mikrós: small). Both optical instruments consisted of two imaging systems: the objective and the eyepiece. However, thanks to differing arrangements of the lenses, the microscope is designed for observing magnified images of small, close objects such as bacteria, while the telescope is intended for distant objects such as the moon and stars.
Galileo Galilei was the first to observe the Moon with his telescope (left) and draw its surface (right). With his astronomic observations, Galilei worked to prove the heliocentric theory of Nicolaus Copernicus (1473–1543), in which the Earth orbits the Sun. Galileo's discoveries were considered heretical, as they completely overturned the Church-sanctioned biblical view of the Earth as the center of creation (the Ptolemaic, geocentric theory). As a result, Galileo was forced to retract his assertions and was placed under house arrest for life. Around 300 years later, "Life of Galileo" by the German playwright Bertolt Brecht dealt with the conflict between scientific research and political and societal conditions. In the play, Galileo states: "The angular sum of a triangle cannot be changed to suit the wishes of the Papal Court". Johannes Kepler (1609, Kepler's Laws) was finally able to prove that the planets move around the sun on eliptical orbits.
It is not entirely clear who built "the first microscope". Was it the Dutch "eye glass maker" Hans Janssen (also known as Jansen or Martens) and his son Zacharias in the year 1590? Or the Italian astronomer Galileo Galilei (1564–1642) who converted his telescope to a microscope in 1609, naming it "Occhiolino"? The astronomer Cornelius Drebbel (1572–1633), who demonstrated his "microscopium compositum" featuring two convex lenses in 1622, is also frequently mentioned. It has also been said that the idea originated with the astronomer, mathematician and "father of modern optics", Friedrich Johannes Kepler (1571–1630). According to another story, two children playing in the workshop of a Dutch "eye glass maker" placed a concave and convex lens together and were thrilled to see how large the weather vane on the church appeared.
One thing that can be said for certain is that the Englishman Robert Hooke (1635–1703) published "Micro-graphia" – a seminal work about microscopy – in 1667, arousing interest in the new observation technique.
Fig. right: The typical "Microscopium compositum" (composite microscope) consisted of a stand, a tube, and at least two lenses – the objective and the eyepiece. The tube consisted of two fiber tubes generally covered with leather that were used to focus. An oil lamp served as illumination. The model shown here belonged to the Englishman Robert Hooke (1635–1703), the discoverer of the cell and perhaps the most versatile scientist of the 17th century.
While the telescope instantly revolutionized astronomy and Galileo explored Jupiter, Venus and the Moon, the microcosm seemed even further out of reach than space. For a long time, the microscope was merely an entertaining toy. The people of the day simply had not yet recognized the potential of the microscope and the world it revealed.
"Microscopic Pleasures for the Eyes and Spirit" and "Insect Entertainment" – as the events were then known – were popular pastimes in the salons of the 17th and 18th centuries. Fleas and lice – which were very common in those days – were popular specimens, and the first simple microscopes were therefore known as "flea glasses".
Around the middle of the 17th century, researchers began discovering the value of the microscope for biology. The Dutch physician Jan Swammerdam (1637–1680) and the English botanist Nehemiah Grew (1641–1712) first combined sectioning methods and microscopy. They dissected insects, sliced up plant matter, and drew unbelievably elaborate and precise illustrations of every detail of their anatomy. In its pioneering days, the microscope gradually evolved into an instrument of scientific research.
Microscopists in the Baroque era discovered sperm, bacteria, cells, red blood corpuscles and the bubonic plague pathogen. And because they looked like small worms, it was believed possible at the time to drive these “Animalcula” (little animals) to extinction. Astonishing methods of fighting these creatures were then devised by scientists and charlatans. For example, extremely loud music and the thunder of cannons was believed to frighten the “Animalcula” so badly that they would flee.
At the time, people still had to learn how to come to terms with this newly discovered realm and find a place for it in the world view dictated by the Church. It was often impossible for them to correctly interpret the new images observed through the microscope with the scientific knowledge of the day. The theory of spontaneous generation, in which small living creatures could arise from putrefaction, was widely believed, while the mechanisms of sexual reproduction of living organisms were still unknown.
In 1350, Konrad von Megenberg, the Canon of Regensburg, Germany, wrote the following: “Bees develop in the stomachs of freshly-slaughtered auroch oxen. The stomachs must be covered in dung for bees to form. Bees also develop in oxen hides that have been covered by soil. Wasps develop in donkey hides.” The first time sperm cells were seen under a microscope, observers were convinced that they contained tiny, complete humans or animals that nourished themselves from the mother's egg.
In the Baroque era, scientists imagined the sperm cell to contain a complete miniature human, the “homunculus”, which subsequently grew in the mother's uterus. Illustration by the Dutchman Nicolaas Hartsoeker (1654–1725).
The shock that could result from the first look though a magnifying glass is documented in a story in “Oculus artificialis teledioptricus”, a book on optics by Johannes Zahn, a German monk and designer of the first portable camera obscura, from the year 1702. The author describes how the Jesuit priest and physicist Christoph Scheiner suffered a stroke while traveling. The eldest of the village in which he died discovered a convex lens, a so-called flea glass, in the priest's belongings. At the time, it was fashionable in noble society to use flea glasses to search for vermin. When the simple villagers looked through the glass, they were convinced that they had seen the devil himself, and refused to give Scheiner a Christian burial, suspecting him of wizardry. In the ensuing argument, the glass was accidentally broken. But instead of the devil, only a flea went hopping off, and Scheiner received a Christian burial after all.
Antonie van Leeuwenhoek (1632–1723) had little formal education and never mastered a foreign language. Nevertheless, he was made a member of the Royal Society for his groundbreaking discoveries. The Dutch cloth merchant was an amateur microscopist and one of the most talented pioneers of microscopy. He studied everything he could get his hands on, and soon realized that the instrument had much more to offer than mere entertainment. He did not even stop at carrying the objects of his studies – lice and fleas – in his trousers pockets, and feeding them with his own blood. He was also the first person to observe and describe bacteria and sperm cells, although he did not know what to make of his discoveries.
Leeuwenhoek was not happy with the existing, assembled microscopes of his day. The glass quality and lens finish was unsatisfactory, delivering poor image quality and no more than 100x magnification. Leeuwenhoek thus learned to grind his own lenses and built microscopes that delivered over 200× magnification and much brighter images than the instruments of his colleagues. They consisted of only one tiny but perfect lens, eliminating the cumulative flaws of multiple-lens systems.
Leeuwenhoek continuously reported his observations, but many scientists of the time did not believe him. He built special microscopes for every object, and none of his peers was able to match the optical quality of his instruments. He kept his best microscopes to himself for his whole life, so it was impossible for anyone to verify his claims. Not even famous visitors such as Czar Peter the Great, George I of England or Frederick I of Prussia were able to talk him into parting with an instrument.
By the time of his death at the ripe old age of 91, Leeuwenhoek had built over 500 microscopes, but took the secret of his art to his grave. It was not until over 100 years later that others matched the brilliance and precision of his lenses.