A quadrant - a quarter of a circle - is an angle-measuring instrument. Usually this is the angle seen from the quadrant between a celestial body and the horizon. That angle is also called the height of the body. This gigantic instrument was manufactured by the renowned Amsterdam cartographer Willem Janszoon Blaeu at the expense of the Leiden professor Willebrord Snel van Royen, better known as Snellius. The latter used it to determine the geographical latitude of Alkmaar and Bergen op Zoom. Because he had also established the actual distance between the locations (by triangulation), he was able to determine the circumference of the earth accurately. After Snellius' death the university bought the quadrant for its Observatory that was in the process of being set up. It was to be the first university observatory in the world. Before that time astronomy had been mainly a hobby of princes.