short treatise of the nature of the elements) (Haarlem, 1621). He was also involved in the invention of mercury fulminate. He also discovered that mixtures of “spiritus vini” with mercury and silver in “aqua fortis” could explode. Drebbel invented a chicken incubator and a mercury thermostat which automatically kept it stable at a constant temperature; one of the first recorded feedback-controlled devices. He also developed and demonstrated a working air conditioning system. The invention of a working thermometer is also credited to Drebbel. Scarlet dye The story goes that, while making a coloured liquid for a thermometer Cornelis dropped a flask of aqua regia on a tin window sill, and discovered that stannous chloride makes the colour of carmine much brighter and more durable. Although Cornelis did not make much money from his work, his daughters Anna and Catharina and his sons-in-law Abraham and Johannes Sibertus Kuffler set up a very successful dye works. One was set up in 1643 in Bow, London, and the resulting colour was called bow dye. The recipe for "colour Kufflerianus" was kept a family secret, and the new bright red colour was very popular in Europe. Optics Drebbel is credited with developing an automatic precision lens-grinding machine, improved telescopes, the first compound microscope ('lunette de Dreubells'), camera obscura, laterna magica, and Dutch or Batavian tears Compound microscope One of the optical devices some historians believe Drebbel invented when he was working for the Duke of Buckingham was the compound microscope. The device appeared in Europe around 1620 with the earliest account being Dutch Ambassador Willem Boreel's 1619 visit to London where he saw a compound microscope in Drebbel's possession, described as an instrument about eighteen inches long, two inches in diameter, and supported on 3 brass dolphins. In 1621 Drebbel had a compound microscope with two convex lenses. Several of his contemporaries, including Christiaan Huygens, credited the invention of the compound microscope to Drebbel. The invention has many counter claims including Dutch spectacle-maker Johannes Zachariassen's claim that Drebbel stole the idea from him and his father, Zacharias Jansen, and claims that Galileo Galilei used his telescope after 1610 as a type of compound microscope. In 1624 Galileo saw Drebbel's design for a microscope in Rome and created an improved version of it to send to Federico Cesi, founder of the Accademia dei Lincei, who used it to illustrate Apiarum, his book about bees. Submarine