How can you make the invisible, visible? One way to do it is through a nineteenth century photography technique called Schlieren Flow Visualization. Better demonstrated than explained, the NPR video above shows Schlieren Flow Visualization in action, rendering visible (after the 2:00 minute mark) the sounds of hands clapping, a towel snapping, a firecracker cracking, and an AK-47 firing off a round. The images, which capture changes in air density, were provided by Michael Hargather, a professor who leads the Shock and Gas Dynamics Laboratory at New Mexico Tech.
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