Grinnell College Physics Museum

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Sonometer

The sonometer is an apparatus by which the transverse vibrations of strings can be studied. It is also called the monocord because it often has only one string. On the box are two fixed bridges, near the ends, and at one end is a pulley. A string, often a steel wire, is fastened at one end, run over the bridges and the pulley, and attached to a weight holder hanging below the pulley. Weights can be added to the holder to produce tension in the wire, and a third, movable bridge, can be placed under it to change the length of the vibrating section of the string. This instrument was purchased from Queen & Co. The date is not known with certainty, but it probably was 1905 or earlier.

Helmholtz Resonators

Before the advent of electronic spectrum analyzers, Helmholtz Resonators were used to detect different frequencies in a sound wave. This set of nineteen resonators was purchased for $70.

Savart Bell and Resonator

The hemispherical bell is made to vibrate by stroking it with a violin bow. If the resonating cylinder is turned toward the bell and its length adjusted by the slide until its resonate frequency matches that of the bell, the sound is intensified. The cylinder can be moved away from the bell and tilted up and down. This piece of equipment cost $20 when it was purchased from Queen & Co. of Philadelphia.

Xylophone Sounding Hammers

ac033 through ac_036

Four Tuning Forks

These four tuning forks, mounted in resonating boxes, were made by L. Landry in Paris. They were purchased in 1900 and the price of the set was $32.

Clamped Square and Round Brass Vibrating Plates

This apparatus came with the holder and two brass plates, one round and the other square. The plates could be made to vibrate, perhaps by stroking with a violin bow or tapping with a mallet, and the resulting sound examined. They could also be mounted with the plate horizontal. Then if a light powder, such as lycopodium powder, was placed on the plate, the nodes of standing waves in the plate when it was bowed or tapped could be seen in patterns of the powder.