Humboldt State University

Robert A. Paselk Scientific Instrument Museum

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Spring Balance Universal Sonometer

W.M. Welch Scientific Company

Chicago

Provenance: Humboldt S-T-C; c.1930

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Usage/History

Used to demonstrate the "laws of vibrating strings" in physics laboratory classes. In this law the relationship of the length of the string (in simplest vibrational mode= one-half the wavelength) the tension on the string in dynes, and the mass/unit length of the string, to the frequency of vibration of a string is described. In use the length of the string is adjusted by moving the bridge until it vibrates in unison with a tuning fork of known frequency. The strings are sounded by striking with a small rubber mallet.

Description

The body of the instrument is about 45" long and 5" wide, made of steel angle-iron rails bolted to cast iron open-work end-pieces. There is a 12" long sheet-steel sound box at the tail end with a black stained hardwood bridge located with brass pins and held in place by the strings of the instrument 20 cm before the opening of the sound-box. The frame and sound-box are all painted in gray wrinkle-finish enamel. A white-enameled steel sheet begins at the opening of the sound-box and extends to end of the instrument. A central scale runs from 20100 cm by 0.1 cm with each cm graduation numbered. Diatonic and equally tempered scales are also marked, from C512­C128. At the top end off the instrument a cast-iron and steel rack extends another 9" and holding three adjustable spring scales with hooks to tension the three strings. Each scale is graduated (red filled engraving) from 0­20 units by 0.25 units, with even graduations numbered. The scales themselves are of bras with white-metal plating. Each scale is attached via a square screw with wing-nut for adjusting tension to the cast iron rack. With the springs fully tensioned the entire instrument would have a total length of 57 1/2". The original adjustable bridge of the instrument is missing: a custom wooden bridge has been substituted. The instrument is in excellent condition barring a pattern of pitting of the white paint on the scale with consequent corrosion, and a chip on the cast-iron of the scale rack.

There is a brass Humboldt S-T-C tag (4857) riveted to the upper left end of the scale.

Research

Minor, Ralph S. Physical Measurements; A Laboratory Manual in General Physics for Colleges. Associated Student's Store, Berkeley (1947) Part II, pp. 94-97

 


HSTC Instrument Collection

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HSTC (1921-34)
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HSC (1935-1953)
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Last modified 1 September 2010