his lectures on a black Arabian horse. Petzval never wanted to communicate anything about his private life, and was therefore relatively inscrutable to others during his lifetime. As Dr. Ermenyi described in his book, Dr. Josef Petzval's Life ". . . he went so far as to always insert a bare point, for example, use the appearing annual yearbook of the Imperial Academy of Sciences, in whatever apart from the names of the members the date and the place appear aforementioned to the birth for itself into this column." At the end of his life he lived in increasingly greater isolation in his "castle" on Kahlenberg, with only his horse for company, although several academies and scholarly societies appointed him a member (member of the Academy of Sciences in Vienna (1846/1849), external member of the Hungarian Academy of Sciences (1873), honorary member of the Union of the Czech mathematicians and physicists (1881), carriers of the French Charles Chevalier Platinmedaille, and others). Disputes Petzval placed very high requirements on himself and others. That was probably connected with his critical, contentious and sarcastic nature, which brought him many conflicts, particularly in the field of mathematics. Petzval had a controversy with Christian Doppler over problems of acoustics, and Doppler responded in 1852 with a book entitled "Remarks Over the Objections Stated by Professor Petzval Against the Correctness of My Theory". In particular he was involved in lengthy disputes with the entrepreneur Voigtländer. These began in 1845, when Petzval raised the issue of fraud for the first time. Because Petzval only held a patent in Austria, Voigtländer shifted his production to Braunschweig in Germany, where he produced about 60,000 Petzval lenses in the following 20 years. Petzval for his part co-operated since 1854 with the Austrian optics producer Dietzler. The latter's lenses were marketed in Austria as the "photographic Dialyt", while Voigtländer marketed the lenses in Germany and Austria as the "Voightländer Orthoskop". After further interference by Voigtländer, Dietzler went bankrupt in 1862. When Petzval threatened legal action, Voigtländer closed his Austrian plant in 1866. Petzval could have then transferred the marketing, but he had renounced working with optics after his home was robbed in 1859 and worked instead on acoustics. In 1862, he also stopped lecturing on optics. Discoveries and inventions Optics Petzval's greatest achievements lie in his work with geometric optics. In 1839, Louis Daguerre presented the Daguerreotype, the first commercially successful