Beeckman's most influential teachers in Leiden probably were Snellius and Simon Stevin.
It was established by Leiden University in 1633, to house the quadrant of Snellius, and is the oldest operating University observatory in the world (before this, astronomy taught at medieval universities tended to be of a more theoretical nature, and any observations were usually done with private equipment rather than at University observatories —see this timeline).
Willebrord Snellius (1580–1626), a Dutch astronomer and mathematician, most famous for the law of refraction now known as Snell's law
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Rudolph Snellius (1546–1613), a Dutch linguist and mathematician at the Universities of Marburg and Leiden
Several have tried to restore the text to discover Apollonius's solution, among them Snellius (Willebrord Snell, Leiden, 1698); Alexander Anderson of Aberdeen, in the supplement to his Apollonius Redivivus (Paris, 1612); and Robert Simson in his Opera quaedam reliqua (Glasgow, 1776), by far the best attempt.