Schlieren experiment - see the invisible
For the open days of EPFL, I had the opportunity to setup an experimental realization of Schlieren experiment using a large (50 cm diameter!) telescop mirror. This setup allows to access the tiny light deflections produced by inhomogeneities in the air, which occurs for instance when one looks at the blurred background above a hot fire.
The video shows for instance the air flow generated by my hand at temperature 37°C in the surrounding air at approximately 20°C. A poster with more explainations can be found here (in french).