Nicolaas Samuelszoon Kruik (Latin: Nicolaus Samuelis Cruquius; 2 December 1678, Vlieland – 5 February 1754, Spaarndam), also known as Klaas Kruik and Nicolaes Krukius, was a Dutch land surveyor, cartographer, astronomer and weatherman. He is remembered most today for the Museum De Cruquius bearing his name.
He was a perfectionist who liked to measure things and he calculated temperature measurements in Fahrenheit from 1706 to 1734. His historical calculations are still used today by the KNMI, the Dutch meteorological institute. He not only measured weather changes in wind speed, rainfall, air pressure, temperature, and humidity, but also measured sea level. His method of visualizing planes of water level to illustrate contours of depth (isobaths) in his map of the Merwede was the first of its kind. He was an advocate of pumping out the Haarlemmermeer (Haarlem lake), which was done a century after his death.
He became a surveyor at the age of 19 and began to draw maps, a lucrative job in his day. Though born in Vlieland, he moved to Delft a few years after he was born and it is there in 1705 that he started his first weather observations. In 1717 at the age of 39, though firmly established as a respected surveyor, he moved to the family farm in Rijnsburg outside Leiden and chose to study in Leiden under Herman Boerhaave, at that time the most famous scientist in the Netherlands. He signed himself in as "Krukius, medical student, born in Delft". Thanks to Boerhaave, Kruik became a member of the Royal Society of London. The secretary of the Royal Society at that time, James Jurin, started the first European network of meteorological weather stations, and the Dutch members played a large part. Kruik was elected a Fellow of the Royal Society in 1724.