vacuum. Other devices did the same for centrifugal force, collisions and laws of momentum, and gravity. Hydrometers, an aerometer, a hydrostatic bellows, a balance and steam pump, several table-top fountains all were used to look into hydrostatic pressure, and capillary attraction. Also shown are a large set of mathematical instruments to measure angles: sectors, a protractor and beam compass. A collection of balances, levers, tackles demonstrate laws of statics. A variety of lenses, prisms, a slit, trays and screens explore optics. About ten screw-barrel and compound microscopes (1710–1780) demonstrate how this young science underwent dramatic progress in few years. A variety of curved mirrors, used as anamorphic toys, show how a deliberately distorted image can be restored back to the original. The room also houses a range of instruments (levers and forceps) used to facilitate childbirth. Lastly, shown are models of three out of five of Archimedes' so called simple machines (lever, inclined plane, wedge, screw and wheel), several hydrostatic balances to demonstrate Archimedes' law and two tables of forces which demonstrate interactions of forces in a horizontal plane. 5 The University of Leiden Linnaeus and Van Musschenbroek Carl Linnaeus published his famous Systema Naturae in 1735, during his 3-year stay in the Dutch Republic, in which he also earned a degree in medicine, and closely worked together with Boerhaave. At display are paintings of Linnaeus and Boerhaave. Also 18th-century models and scientific measuring instruments: models that demonstrate basic physics principles, and instruments: several antique thermometers, a barometer, a theodolite and several pyrometers. Also two antique globes (one showing the heavens, one earth) and two mirror telescopes. The room is conamed after the brothers van Mussenbroeck: Pieter a professor, credited with the invention of the first capacitor in 1746: the Leyden jar, and Jan a famous instrument maker, who shipped his hand crafted precision thermometers all over Europe. 6 Wonders of nature Over 30 antique microscopes are shown, most from the 18th century, in a large variety, with different solutions for lighting the subject and minimization of lens defects (e.g. chromatic aberration): simple, compound and reflecting microscopes, so called English microscopes (renowned for their quality), solar microscopes (which project their image on a wall, using sunlight only). Several wooden cabinets with microscopic slides are testimony of the craftsmanship than went into collections of ready made samples, which at the time were highly fashionable among well-to-do citizens who took an interest