Zacharias Janssen

Zacharias Janssen bigraphy, stories - Dutch scientist

Zacharias Janssen : biography

Zacharias Janssen (also Zacharias Jansen or Sacharias Jansen) (b.1580-88, d.pre-1632 to 1638) was a Dutch spectacle-maker from Middelburg associated with the invention of the first optical telescope. Janssen is sometimes also credited for inventing the first truly compound microscope. However, the origin of the microscope, just like the origin of the telescope, is a matter of debate.

Illegal activities

In the years 1613–1619, Janssen was tried several times for counterfeiting coins. Janssen grew up right next to the Middleburg mint where his brother-in-law worked. These circumstances made it very easy for Janssen to mimic the process of manufacturing money. He fled to the neighbouring village of Arnemuiden to avoid the high penalties for counterfeiting coins.

However, he continued counterfeiting coins in Arnemuiden. In 1619 he was apprehended for owning several devices he counterfeited coins with. Normally, one would have been sentenced to death for this crime. However, since the father of the Arnemuiden bailiff was found to be an accessory, it turned out better for Janssen. Thanks to this, the process was delayed to such an extent that Janssen was able to flee yet another time. Eventually, the case was dismissed. Janssen returned to Middleburg in 1621.

Historical record

Janssen’s life was documented by the many investigations on the subject before the Second World War. Many of the Middelburg archives were destroyed by a devastating bombardment on May 17, 1940, during the Nazi invasion of the Netherlands. If there had never been profound investigations, very little would be known of Janssen’s life at all, since all files were lost in the fires following the bombardment.


Janssen was born in The Hague with date of birth commonly given as 1580David Whitehouse, Renaissance Genius: Galileo Galilei & His Legacy to Modern Science – 2009, page 67 although some sources place it as late a 1588.Ari Ben-Menahem, Historical Encyclopedia of Natural and Mathematical Sciences – Volume 1 – 2009, page 5294 His parents were Hans MartensSource: a book by Huib J. Zuidervaart which is to be published in the spring of 2008. The Public Observatory Philippus Lansbergen in Middelburg has already been shown a first version of this book. (who may have had the occupation of a peddler) and Maeyken Meertens, both probably from Antwerp, Belgium. He grew up with his sister Sara in Middelburg, at the time the second most important city of the Netherlands. He was known as a "street seller" who was constantly in trouble with the local authorities, and later became a spectacle-maker.

He himself stated he was born in The Hague on the marriage file of his first marriage, with Catharina de Haene, on October 23, 1610. When this file was refound by Cornelis de Waard in 1906, De Waard found the following excerpt: Sacharias Jansen, j.g. uut Den Haag, translated into modern English: Zacharias Jansen, bachelor from The Hague Before, it was often thought that Janssen was a native of Middleburg. In 1612, Zacharias and Catharina had a son they named Johannes Zachariassen.

Following the death of Janssen’s first wife in 1624, he married Anna Couget from Antwerp, who was the widow of a Willem Jansen (probably a relative of Jansen). He moved to Amsterdam in November 1626. Janssen has been given a death date as late as 1638 although his son Johannes declared his parents had died by the time of his marriage in April 1632.


By choosing the profession of spectacle-maker, Janssen entered a very competitive and secretive trade. These factors may have played a role in Janssen’s claims of invention of the telescope and the microscope since he and Middelburg spectacle maker Hans Lippershey were direct competitors who practically lived next door to each other. Janssen’s attribution to these discoveries is debatable since there is no concrete evidence as to the actual inventor, and there are a whole series of confusing and conflicting claims from the testimony of his son and fellow countrymen, in different investigations that took place 20 to 65 years after the claimed invention.Albert Van Helden, Sven Dupre, Rob Van Gent, The Origins of the Telescope – 2011, page 43