Frans Kessler (c. 1580–1650)

• Was a German portrait painter, scholar, inventor and alchemist.
• Kessler was living in the Holy Roman Empire during the 16th and 17th centuries.
• He wrote a number of books and pamphlets: a book on stoves, on making sundials, on using a "sector" or "proportional instrument" (a simple calculator).
• In the 1620s and 1630s, he was a portrait painter in Cologne, Germany.
• He wrote a book called Unterschiedliche bisshero mehrern Theils Secreta oder verborgene, geheime Kunste (Various until now mostly Secreta or hidden, secret arts), which was published in Oppenheim in 1616.
• The first five chapters of this book deal with communicating via a crude Aldis lamp.
• In the same year he built an improved diving bell.
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