Jacobus Barnaart

[1] His father was a merchant, silk cloth manufacturer, and regent of the local orphanage.

Following in the footsteps of his father, the younger Barnaart became a merchant, but also showed an interest in astronomical measurements.

Barnaart's interest in astronomy led to his setting up an astronomical observatory on top of the Oval Room, although he was advised by Martinus van Marum that this would not be a practical place due to vibrations, which could lead to inexact measurements.

[3] The Teylers astronomical observatory was constructed on top of the Oval Room, but in a smaller version than initially planned.

Diaries of Barnaart have been preserved,[2] describing his experiences from age 11 onward, which includes some of his astronomical observations.