of mathematics there in 1837, and worked until 1877 as a professor of mathematics. Apart from mathematics, he was also concerned with mechanics, ballistics, optics, and acoustics. His lectures on the theory of algebraic equations, which integrated linear and differential equations with constant and variable coefficients, ballistics, acoustic theory, and other areas were high quality and became well attended. Petzval moved into a rented abandoned monastery at Kahlenberg mountain. He founded his own glass-sharpening workshop there. His lenses became world-famous because Petzval was also a skillful lens sharpener and precision mechanic. In 1840, he designed his famous portrait lens. 1845 brought disputes with the entrepreneur Peter Wilhelm Friedrich von Voigtländer (1812–1878) over who had the right to produce Petzval's lenses. In 1859, Petzval's home was broken into, and his manuscripts — a result of many years of research — were destroyed. Petzval never managed to reconstruct the lost documents. His most refined technical book on optics, lost with his manuscripts, would never appear in print. From then on, he primarily concerned himself with acoustics and began to withdraw from society. His enterprise with Carl Dietzler failed in 1862 (see further below); Dietzler died in 1872. In 1869, at the age of 62, Petzval married his housekeeper, but she died four years later. In 1877, he stopped lecturing, withdrew to a monastery on Kahlenberg, and became a hermit. Petzval died in Vienna in 1891, nearly forgotten, embittered, and destitute. His grave is in the Viennese central cemetery. His bitterness at the end of his life can probably be traced, on the one hand, to his continuing controversy with Voigtländer, the loss of his manuscripts, and his business failure; and on the other hand, to the fact that he was never really acknowledged for his lifelong work in the field of optics. Just before his death, Petzval was reported to have said: "I defeated the light, I have it firmly in hand, because there is much darkness in the world too." Private life and hobbies Petzval was a good sportsman and rider. As a young child, he often traveled with his family to the High Tatras, and was also a dedicated athlete. In Vienna, he was for a long time the best fencer and ring fighter in the city. He also inherited an excellent talent for music from his father. Allegedly, while he was a lecturer in Vienna, he always rode to