|Interrelationships between Coers, Onnes, and Roest families.|
In this drop chart, the individuals marked in blue are distant cousins. Let's begin with someone we've visited before, my fourth cousin twice removed, physicist Heike Kamerlingh-Onnes (1853-1926). His parents were Harm Kamerlingh-Onnes (1819-1880) and Anna Gerdina Coers (1829-1899), linking two of these families.
Heike's uncle Jacob Jan Coers (born 1834) worked in the printing and lithography business in Arnhem, establishing in the 1850's the firm Letter- en stereotypegieterij, kunstboekdrukkerij en graveerinrichting Onnes, de Boer en Coers. One of his partners in that company was Hermannus Barteld Onnes (1807-1863), first cousin once removed of Heike Kamerlingh-Onnes.
In the 1880's, Jacob Jan Coers took on his brother-in-law, Gerrit Roest (1857-1908), as a partner in the firm Coers & Roest, a company that still does business today.
The interrelationships between these families continue: Gerrit Roest married Heilina Froukelina Onnes (born 1859), a first cousin of Heike Kamerlingh-Onnes. And Jacob Jan's brother Gerrit Thomas Coers (1826-1903) married Agatha Henderika Onnes (1831-1895), a second cousin of Heike Kamerlingh-Onnes.