Images(7)

variation compass

Date1765

Inventory Number0025

ClassificationMagnetic Compass

Subject

Maker Edward Nairne 1726 - 1806

User John Winthrop 1714 - 1779

User Samuel Williams 1743 - 1817

Cultural Region

Place of Origin

Place of Use

Dimensions36.8 x 23.5 x 4 cm (14 1/2 x 9 1/4 x 1 9/16 in.)
radius of arm: 36.8 cm (14 1/2 in.)

Material

Bibliography

The Apparatus of Science at Harvard, 1765-1800

DescriptionThe horizontal brass frame of this instrument has a curved limb subtending an arc of 40°. The whole instrument is supported on three leveling screws. The scale engraved on the limb is marked in degrees subdivided every 20' and numbered twice by tens from 0°-30° and from 30°-0°. The index arm with vernier moves along the limb. A tangent screw is used to make fine adjustment of the index arm.

The rectangular brass box has a silvered bottom and a glass cover. It contains a magnetized needle attached to the index arm. The silvered surface is decorated with a foliage design. The holes below the box could have been used either to fix a level or a small magnifying glass to assist in aligning the variation needle. Some screws have small pre-determined punched dots for dismantling purposes. A very uncommon instrument by Nairne.

In Collection(s)

Signedon arc: Nairne London

Curatorial RemarksXRF analysis of the metals was done by Katherine Eremin and Sara Schechner in August 2007.

FunctionThis kind of instrument is used to measure declination of the earth's magnetic north in relation to the true geographical north. A compass needle has two motions: horizontal (to determine the magnetic north) and vertical, towards the center of the earth, what is called inclination or dip of the needle. Since the magnetic poles shift gradually and irregularly, these two motions varies with time and according to where you stand at the surface of the earth. For an accurate picture of the earth's magnetism, these two motions need to be taken into account. The variation compass can measure precisely the magnetic declination on a day-to-day basis.

ProvenanceJefferson Physical Laboratory, Harvard University; transferred to CHSI May 1948.

Historical AttributesThis instrument was bought by Harvard from Nairne in 1765. It cost £10.18.0. It came in a mahogany box lined with green cloth, lock and key. It has been lost since then. At Harvard, Samuel Williams, the Hollis Professor, assisted by Stephen Sewall, the Hancock Professor of Hebrew and other Oriental Languages, published readings taken on this instrument (and the Nairne dip circle, 0026) in the first volume of the Memoirs of the American Academy of Arts and Sciences (1785). In 1786, Williams was appointed by the General Court of Massachusetts "to make some observations to determine the running of the dividing line between the States of Massachusetts and New York." He was "allowed to take with him the Variation Compass [0025], Hadley's Quadrant [0007] and Kalm's Travels, belonging to the College." Before the fire destroyed Harvard's apparatus in 1764, Harvard had received a variation compass from London Merchant, Mr. Gilbert Harrison in late 1761 or early 1762. Thanks were given by the Corporation on January 5, 1762. (see related references)