Cornelis Vallensis

In 1689, Leeuwenhoek was persuaded to tell the Royal Society the identity of the people in Delft who he kept referring to as witnesses to his observations. These people had been coming to Leeuwenhoek's house for years to peer through his lenses. They were able to see what he saw. The three that Leeuwenhoek mentioned were Vallensis, Cornelis Gravesande, and Anthony Heinsius.

Leeuwenhoek lived on the corner of the Nieuwstraat, a short street between the Nieuwe and Oude Delft grachten. Vallensis lived at the other end, across the Oude Delft from the Sint-Hippolytuskapel. The property had been in his wife's family, the Berensteyns, for many years.

His grandfather, Dr. Jacob van den Dael / Vallensis (1570-1640), was personal physician to the Princes Maurits and Frederik Hendrik of Orange.

His father, Dr. Theodorus Vallensis (1612-1673) joined the Veertigraad in 1647. He did two stints as magistrate, 1648-1650 and 1658-1660. He was a mayor of Delft in the rampjaar, 1672, installed as a result of the replacement of half of the Vertigraad by men favoring the House of Orange. The next year, the final year of his life, Vallensis was a curator of Leiden University, replacing the recently assassinated and mutilated Cornelis de Witt.

Cornelis Vallensis went to Leiden University in March 1666 but did not get his doctorate until 1683.

Back home in Delft, he joined the Veertigraad in 1681.

When he served as a magistrate from 1682-1686, he came into constant contact with Leeuwenhoek, by then the world-famous member of the Royal Society.

Vallensis was also a trustee of the orphanage in 1688, and Adjunct ter Dagvaart in 1691 in the final year of his life.

His nephew Dirk, son of his brother Jacob, was on the Veertigraad after 1703 and also served as a magistrate in 1722 and 1723 and Adjunct ter Dagvaart in 1724, the final year of his life.