Adjustable forks were used primarily as teaching instruments, although they may have had medical applications as well. These instruments seem to have been introduced in the 1890s and were common in 20th century high school laboratories. Adjustable forks could take the place of several individual forks and had the added advantages of being relatively inexpensive and quite durable. Moving the adjustable weight on each tine changes the tone by effectively changing the tines' length. Thus moving the weight down the tine raises the tone, and moving the weight up the tine lowers it.
Lord Kelvin’s harmonic synthesizer is basically Henrici’s harmonic analyzer in reverse. Originally designed as a tide predictor in 1873, the system can combine numerous component waves—in some devices, up to 64 separate components—into a single curve. It is based on the earlier pin-and-slot device, which produces simple harmonic motion with the turn of a crank.
The Smithsonian's National Museum of American History houses literally millions of objects which preserve and illustrate our nation's rich history. Among the many stories that these objects tell are the ways that Americans have learned about science. This site is designed to help students and teachers explore a unique and beautiful collection of instruments used to teach Acoustics - the science of sound. These historic instruments were designed to be engaging and to challenge students to think in new ways about the physical world.