Immagini

DESCRIPTION

Exhibit 351 is a magnetometer which can measure the declination and the horizontal component of the earth's magnetic field. It is characterized as unithread because the magnet is suspended at its center of gravity by a long string. The measure of the declination requires two distinct determinations, the meridian of the local magnetic field, found by observing the orientation of the magnet in the horizontal plane, and the geographic meridian, found by observing the passage of the sun or of a star. For this reason, the magnetometer is composed of several interchangeable elements. The instrument is supported on a circular dark brass base graduated from 0° to 360° marked every 10°, in intervals of 20 minutes and readable in divisions of 20 seconds by using verniers. Above the base there is a support with a bubble level for a mirror.

At the center of the base there is a metal bridge on which rests a wood box that has two small circular glass windows on opposite sides while the other sides are openable being hinged at the base. Above the box one mounts a long glass cylinder on the summit of which is hung the metallic wire that suspends the magnet.

Between the box support and the circular base there are two hooks for inserting exhibit 422. Near the glass cylinder there is a hole for a thermometer for measuring the temperature inside the box.

Inside the box there is a lever for reducing the oscillations of the magnet.

The orientation of the base can be fixed with a micrometric screw.

For a detailed description of its use, consult reference 1.

ISCRIZIONI

1. Sul basamento è inciso: Ing. A. Salmoiraghi, Milano, 12942

BIBLIOGRAPHY

• [1] Prof. Ciro Chistoni,"Magnetometro Unifilare dei Seni",Annali dell'Ufficio Cebtrale Meteorologico e Geodinamico Italiano,serie II,14 (parte I,1892),100-120
• [2] M. Basso Ricci et al. "Due secoli di strumenti geomagnetici in Italia (1740 -- 1971)", 1997, Bologna, Pagine: 146 - 151
• [3] Worsnop B.L., Flint H.T.,"Advanced Practical Physics for Students", Asian edition,1961, Chapter XVII: Terrestria Magnetism
• [4] Balfour Stewart, Haldane W.W.,"Lessons in Elemantary Practical Physics",VOL. II. Electricity and Magnestism, Macmillan and CO., London. 1887. Chapter II

Dati Catalografici