Meeting Review, April 2003
|other meeting reports||4/10/03 Meeting Highlights
by Bob Zurek
On April 10, 2003 Dr. Marc Rothenberg gave a presentation to the AES Chicago Section titled "Joseph Henry, Lecture Halls, and Fog Horns: Acoustics in the Service of Society." Dr. Rothenberg began his presentation by reading from memorials written to Joseph Henry after his death. While the memorials pointed out how well known Henry was in his time, today if known at all, Henry is more known for the unit of measure named after him than anything he accomplished in his lifetime.
Dr. Rothenberg discussed Joseph Henry’s life from childhood, through his teaching appointments at Albany Academy and Princeton University (then called the College of New Jersey), to his becoming the first secretary of the Smithsonian Institution. Dr. Rothenberg gave insight into Henry’s views and approach to science and engineering. He stated how Henry could find his inspiration for study anywhere around him, as evidenced by his decision to explore molecular bonding and tensile strength after observing children blow soap bubbles. His study prior to working in acoustics, lead him to extensive work in electromagnetism and astronomy. Henry is credited as the first to use insulated wire in the windings of his electromagnets, and the discovery of the first transformer, and reciprocating motor.
Dr. Rothenberg went on to discuss Henry’s contribution to acoustics, beginning with his work in the 1840’s in room acoustics. Henry wanted the lecture hall in the Smithsonian to be the best lecture hall science could produce. Dr. Rothenberg discussed the rooms that Henry worked on in Washington D.C. including the capitol building and the Smithsonian lecture hall. Dr. Rothenberg stated that although the Smithsonian lecture hall was the best in the country, it only lasted from 1854 until 1865 due to a fire. During this time Henry discovered that an acoustic echo could only be distinguished after sound traveled 100 feet, which agrees with the well-understood phenomenon that echo delayed 80ms or more results in poor intelligibility. It was also during this study that Henry discovered the “precedence effect.”
Dr. Rothenberg discussed the acoustic work that Henry did in his later life on the development of effective foghorns. A major part of this work was done while he was on the US lighthouse board and concerned the effect of wind on sound as well as the amplitude variation of sound over water.
Dr. Rothenberg ended his prepared presentation with the comment that Joseph Henry always asked “why” regardless of his age. Following the presentation Dr. Rothenberg answered questions on the life and work of Joseph Henry.