Zacharias Janssen

Dutch lens maker

• Born: c. 1580
• Birthplace: The Hague, the Netherlands
• Died: c. 1638
• Place of death: Amsterdam, the Netherlands

Janssen was a Dutch optician with a claim to having invented both the telescope and the microscope. With improvements by scientists such as Galileo, Cornelius Drebbel, and Antoni van Leeuwenhoek, the telescope and microscope soon became the most important scientific instruments in astronomy and biology.

Primary field: Optics

Primary inventions: Compound microscope; telescope

Early Life

Zacharias Janssen (zak-a-RI-ehs YAHN-sehn) was born in the Netherlands around 1580, although his birth has been variously placed in the years 1580 to 1590. Holland was besieged by Spain during this period, and in the 1580’s Janssen’s family fled to Middelburg, located in the Dutch province of Zeeland. His father, Johannes (Hans), was a skilled optician and owned a spectacles shop in Middelburg. Johannes, perhaps with the assistance of Zacharias, experimented fruitfully with the magnification of spectacle lenses. After the death of Johannes around 1592, Zacharias inherited his father’s optical shop. He also peddled his optical goods at town fairs and markets. Zacharias was a childhood friend and neighbor of William Boreel, whose father was a director of the Dutch mint; Zacharias apparently observed enough that he could later become a counterfeiter. On November 6, 1610, Zacharias married Catharina de Haene. Their son, Johannes Sachariassen, was born the following September.

Life’s Work

Janssen engaged in two moneymaking ventures in addition to his work as a lens crafter. The first was the making of a telescope and microscope, which would give his name historic recognition; the second was counterfeiting, which would jeopardize his life. The scientific instruments developed from his lens-crafting trade while he was young; his career as a counterfeiter started later.

The precise details of the invention of the telescope and the microscope cannot be definitively ascertained. There were precursors of the telescope in Italy in the 1590’s before the first real telescopes appeared in Holland in the 1600’s. At least three Dutch lens makers have claims to the invention of the telescope—Janssen, Hans Lippershey, and Jacob Metius. Historians such as Cornelis de Waard and Albert Van Helden have described a scenario crediting Janssen as the first inventor based on circumstantial evidence and informed speculation.

The invention of the telescope resulted from the expertise of Dutch opticians in crafting spectacle lenses. Convex eyeglasses were invented in late thirteenth century Italy to assist elderly people suffering from presbyopia. Concave lenses were invented later for myopia. A convex lens is thick in the middle and curves outward; a concave lens is thinner in the middle and curves inward; a planar lens is flat. The angle of the lens determines the refraction of light and thus the magnification. In the fifteenth and sixteenth centuries, lens-grinding techniques and the quality of glass for both convex and concave lenses steadily improved. As part of his explorations in magnification in the beginning of the seventeenth century, Janssen probably put a stronger concave lens against his eye and a weaker convex lens some distance apart. When he looked through the two lenses, he saw distant objects magnified. Connecting the two lenses with a tube, Janssen was able to make the first telescope, probably in the year 1604. It is also possible that Janssen had heard about or seen a similar instrument that had been made in Italy several years before, perhaps as early as 1590. Because this telescope employed glass lenses to refract light, it would come to be called a refracting telescope. Because an obvious use was for the military to spot enemy forces on land and sea, the telescope was first known as a spyglass.

Over the next few years, Janssen may have worked secretly to increase the magnification of the spyglass, to about three times. Historians believe that Janssen’s character was such that when his spyglass had reached a sufficient magnification, he would try to quickly profit from his invention rather than undertake the legal machinations of obtaining a patent. In September of 1608, he was trying to sell a telescope at the Frankfurt Fair among his other optical wares, although a potential customer complained that the glass was cracked and the instrument too expensive. A few weeks later, on October 2, 1608, a neighboring spectacles maker, Hans Lippershey, petitioned the Dutch States-General in The Hague, the governing body of the Dutch Republic, for a patent for a binocular telescope. This patent application was denied because the investigating committee discovered that the art of making a spyglass telescope was already known to a young man. This young man was probably Janssen. Janssen, learning of Lippershey’s application, may have gone to The Hague to present himself as the first inventor. Although denied a patent, Lippershey was commissioned to make two more binocular instruments. A few weeks later, yet another Middelburg lens maker, Jacob Metius, applied for a patent for a spyglass and was also denied. One of these early spyglasses was presented to Prince Maurice of Nassau, the Dutch stadtholder, and several others were soon dispersed around Europe.

The best claims for the invention of the telescope by Lippershey or Metius are their documented patent applications; for the claim of Janssen, it is the testimony of his son, Johannes Sachariassen, and of his childhood friend, William Boreel. In 1655, Boreel, serving as Dutch envoy to France, testified that Janssen was the inventor of the telescope. Boreel also claimed that Janssen was the first inventor of the compound microscope. Like the refracting telescope, a compound microscope consists of two lenses: an eyepiece and an objective lens, which refract light to magnify the image. The invention of the compound microscope probably developed from that of the telescope, as they both follow the same principle, except that with the microscope the object is placed on the objective lens. Therefore, it is plausible that the same person who invented one quickly developed the other. It is even possible that the same instrument served as both a rudimentary telescope and microscope. Boreel claimed to have seen one of Janssen’s original microscopes in 1619. He described it as a tube one and a half feet long and two inches in diameter. The viewer looked through the glass at the top down to the minute object resting on an ebony disc at the bottom of the tube.

After 1610, Janssen’s questionable activities increased. He was in legal trouble for unpaid drinking bills and for assault. In 1613, he was arrested for counterfeiting, but on April 22 the municipal court of Middelburg merely fined him, probably because he was counterfeiting Spanish copper quarters. Relocating to the town of Arnemuiden, he advanced to the more profitable counterfeiting of gold and silver coins. In 1618, Janssen was sentenced to death for counterfeiting. He avoided the capital sentence by escaping to Middelburg. Janssen’s wife died in 1624, and he married Anna Couget a year later. After failing to meet a loan obligation on May 1, 1628, he was bankrupt and his property was auctioned. He died about ten years later, probably in Amsterdam.

Impact

The details of the invention of the telescope and microscope are lost to history, but the impact of their invention is clear. The telescope and microscope were invented by skilled Middelburg lens grinders in their workaday shops, without a theoretical knowledge of optics. It was some of history’s greatest scientists who used their theoretical knowledge to improve these instruments and make astounding discoveries.

Eyeglasses were invented in Renaissance Italy, giving rise to speculation about the possibility of magnification through the manipulation of glass lenses. By the beginning of the 1600’s, the skill of Dutch opticians had reached the point where the discovery of a simple refracting telescope and compound microscope was likely. Janssen may have been the first to invent a telescope in the years 1604 to 1608, but it may well have been Hans Lippershey or even Jacob Metius, or all three simultaneously. Certainly it was Lippershey who recorded and publicized the invention by applying for a patent in October, 1608. Although the States-General denied Lippershey his patent, its examining committee brought the new discoveries to the attention of the Dutch and soon all of Europe. The princes of Europe conceived of the telescope as a spyglass to obtain advantages over military enemies and assist navigation. Galileo had another idea. Relying on his superior knowledge of the theory of optics and refraction, he made an improved telescope within a year of learning of the Dutch discovery and aimed it at the sky. A half century later, the Dutch lens grinder Antoni van Leeuwenhoek and the English scientist Robert Hooke made improved microscopes and observed bacteria swimming in drops of water.

By meticulous, unaided observation, astronomers such as Nicolaus Copernicus, Johann Bayer, and Tycho Brahe had plotted the solar system to a remarkable degree, but with the telescope, scientists such as Galileo, Johannes Kepler, and Isaac Newton were able to reveal the secrets of the planets, Sun, and stars, and of light and gravity that bind them. With the microscope, the fundamental life of microorganisms was revealed. From the commercial grinding and manipulation of lenses by opticians at the dawn of the Dutch Golden Age came the instruments that have transformed science.

Bibliography

Andersen, Geoff. The Telescope: Its History, Technology, and Future. Princeton, N.J.: Princeton University Press, 2007. Introduction to all aspects of the modern telescope, crediting the invention of the refracting telescope to Lippershey.

Asimov, Issac. Eyes On the Universe: A History of the Telescope. Boston: Houghton Mifflin, 1975. Engaging account by the world-famous writer on science. Asimov prefers to credit Janssen with the 1604 invention of the telescope and Lippershey for putting it into use.

Croft, William. Under the Microscope: A Brief History of Microscopy. Hackensack, N.J.: World Scientific, 2006. Well-written history of the microscope; credits Johannes and Zacharias Janssen with its invention.

Helden, Albert Van. The Invention of the Telescope. Philadelphia: American Philosophical Society, 1977. Relies on the original sources uncovered by Cornelis de Waard and published in his De uitvinding der verrekijkers (1906) for the most thorough discussion of the invention of the telescope. These original sources are translated and included in the appendix.

Ilardi, Vincent. Renaissance Vision from Spectacles to Telescopes. Philadelphia: American Philosophical Society, 2007. Scholarly history of eyeglasses, leading to the invention of the telescope.

Panek, Richard. Seeing and Believing: How the Telescope Opened Our Eyes and Minds to the Heavens. New York: Viking Press, 1998. Popularly written history of the telescope from its origins with Dutch opticians.

Reeves, Eileen. Galileo’s Glassworks: The Telescope and the Mirror. Cambridge, Mass.: Harvard University Press, 2008. Explores the period from the invention of the telescope to its reception and improvement by Galileo.

Ruestow, Edward. The Microscope in the Dutch Republic: The Shaping of Discovery. New York: Cambridge University Press, 2004. Scholarly study of the relationship between culture and science in the lives of the Dutch Golden Age pioneers of the microscope.

Watson, Fred. Stargazer: The Life and Times of the Telescope. Cambridge, Mass.: Da Capo Press, 2005. Dramatically told history of the telescope. Emphasizes the role of Janssen’s unsavory character in obscuring the details of the telescope’s invention.