Adjustable tuning fork, Science Teaching Collection
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. To produce a pure tone, it was important that the weights on both tines be precisely opposite each other.
Source: Steven Turner; Curator, Physical Sciences, National Museum of American History, Smithsonian Institution.
Picture: Steven Turner
