with two convex lenses, for which there was a constant demand. At the request of Roman-German Emperor Ferdinand II in 1619, he went to Prague again to tutor his sons and was taken prisoner after the Battle of White Mountain and the capture of Prague in 1620, where he also lost his fortune. In 1622 Constantijn Huygens stayed as a diplomat for more than one year in England. It is quite possible that he learned the art of glass grinding at this time from Drebbel, and that he passed this knowledge to his second son Christiaan Huygens, who became a prominent Dutch mathematician and scientist. The English natural philosopher Robert Hooke may have learned the art of glass grinding from his acquaintance Johannes Sibertus Kuffler, the son-in-law of Drebbel. Towards the end of his life, in 1633, Drebbel was involved in a plan to drain the Fens around Cambridge, while living in near-poverty running an ale house in England. He died in London. In keeping with traditional Mennonite practice, Drebbel's estate was split between his four living children at the time of his death. Works The Edison of his era, Drebbel was an empirical researcher and innovator. His constructions and innovations cover measurement and control technology, pneumatics, optics, chemistry, hydraulics and pyrotechnics. He registered several patents with the Dutch "Staten Generaal". He also wrote essays about his experiments with air pressure and made beautiful engravings; including The Seven Liberal Arts on a map of the city of Alkmaar. He was involved in making theater props, moving statues and in plans to build a new theater in London. He worked on producing torpedoes, naval mines, detonators that used glass Batavian tears, and worked on fulminating gold (aurum fulminans) as an explosive. He was known for his Perpetuum Mobile, built an incubator for eggs and a portable stove/oven with an optimal use of fuel, able to keep the heat on a constant temperature by means of a regulator/thermostat. He designed a solar energy system for London (perpetual fire), demonstrated air-conditioning, made lightning and thunder ‘on command’, and developed fountains and a fresh water supply for the city of Middelburg. He was involved in the draining of the moors around Cambridge (the Fens), developed predecessors of the barometer and thermometer, and harpsichords that played on solar energy. Chemistry Drebbel's most famous written work was Een kort Tractaet van de Natuere der Elementen (A