Query: What did former BYU graduate Harvey Fletcher invent?
Context: BYU alumni in academia include former Dean of the Harvard Business School Kim B. Clark, two time world's most influential business thinker Clayton M. Christensen, Michael K. Young '73, current president of the University of Washington, Matthew S. Holland, current president of Utah Valley University, Stan L. Albrecht, current president of Utah State University, Teppo Felin, Professor at the University of Oxford, and Stephen D. Nadauld, previous president of Dixie State University. The University also graduated Nobel Prize winner Paul D. Boyer, as well as Philo Farnsworth (inventor of the electronic television) and Harvey Fletcher (inventor of the hearing aid). Four of BYU's thirteen presidents were alumni of the University.