In order to make the tuning forks (Resonators) vibrate, Helmholtzused an in termittent electrical current to be conducted through the coils which would give as many electrical shocks as the lowest forks made vibrations in a second. The shock makes each fork magnetic for a moment, which attracts the fork to the mag net and causes it to vibrate.
When the system is in motion, all of the Resonators are closed, such that n o tones are heard with the exception of a slight humming from the forks. By ope ning the resonators, one by one, each new tone is heard, and different combinat ions of resonators yield different tones -- and vowel sounds.
Design and Analysis of the Interrupting Fork
This apparatus is created to produce an intermittent current of exactly det erminate periodicity. There are two cups of mercury which are dipped from a wir e fastened to each prong of the fork; however, only one of the cups (d) is used for conducting the current inwards.
".....the interrupting apparatus is so arranged that each vibration of the fork makes the current twice; once when the upper prong dips into the cup of mer cury h, and once when the lower prong dips into the cup i."
"When the prongs of the fork move apart, the conduction will be broken at h, and after a short interval again completed at i, so that the current now pass es from g through the lower prong of the fork to i." In this instance, a powerf ul spark would thereby be emitted, so condensor c is inserted to calm this effec t.