String Drivers
   Electrically driven tuning forks were used to set up standing waves on strings. One end of the string was fastened to the fork tine, and the other went over a small pulley and was terminated with a pan on which weights could be placed. The frequency of the tuning fork is fixed, and so the proper wavelengths are controlled by varying the speed of the wave on the string. Since this is proportional to the square root of the tension in the string, the experimenter must carefully place small weights onto the pan until the best standing wave is obtained. Other driven tuning forks can be seen in the acoustics pages. This fork was made by Central Scientific and is in the Greenslade Collection.

   From the 1929 Cenco catalogue, which shows a slightly more modern version of this fork: "This is a fork of generous dimensions and sturdy construction. Because of these qualities it commends itself for use on the lecture table, where its size and driving power render it, and the experiments performed with it, visible through a large room; and insures proper continuous operation without the troublesome adjustment encountered with earlier forks. ...The prongs are drilled on the ends to receiver ... mirrors, so that with two forks Lissajous' figures may be observed. One fork is provided with a stylus [held under the screw on the further tine], and the other has a knurled screw for attaching a cord, as in Melde's experiment. ...$17.50" The mirrors were $3.00 for a pair.

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