Schlieren physics developed out of the need to produce high-quality lenses devoid of these inhomogeneities. Schlieren imaging is a method to visualize density variations in transparent media. Until 1415, Schlieren belonged to Habsburg. This research particularly resulted in the development of the Schlieren technique. There are 6262 households in Schlieren. See, for example, shadowgraph and schlieren photography. The importance of the schlieren imaging technique is prominent in HIFU research and development. The schlieren effect is often used in video projector technologies. The album cover is an example of schlieren photography demonstrating the 'solid' nature of air. At 3 October 1909 in Schlieren, the fourth Gordon Bennett Cup in ballooning was held. Schlieren has an unemployment rate of 4.23%. Toepler's original system was designed to detect schlieren in glass used to make lenses. Complete schlieren optical systems can be built from components, or bought as commercially available instruments.