Snellius' Quadrant

A quadrant was a straightforward angle measurement device developed in the pre-telescope area. Placed vertically it measured elevantion, placed horizontally it measured azimuth. Tycho Brahe obtained a precision of about 1' with such instruments. The quadrant shown was the first instrument of Leyden Observatory, bought in 1629 by the first director Jacob van Gool (Golius) from the widdow of Willebrord Snel van Royen (Snellius). The man most known from the refractive index and his law. It was constructed for him in 1610 by W. J. Blaeu, the famous map maker. This quadrant was always a decorative object in the observatory, but is now on display in Museum Boerhaave.