City Allergy

Category: Allergy Factoids  

Coughing imaged

Schlieren is German for “streaks”; in this case it refers to regions of different densities in a gas or a liquid, which can be photographed as shadows using a special technique.  To map airflow, the expelled air, traveling at 18 miles per hour, mixed with cooler surrounding air and produced “temperature differences that bend light rays by different amounts.”