Donald Earl Coles (MS '48, PhD '53), professor of aeronautics, emeritus, passed away on May 2 at age 89. Coles was a master instrument builder famed for his ingeniously designed and precisely executed experiments. His doctoral dissertation provided the first comprehensive set of data on supersonic boundary layers. A few years later, he made an important addition to the theory of turbulent boundary layers that he christened "the law of the wake."