Accession No

3282

Brief Description

dip circle and accessories in a box, by Henry Barrow and Company, 1842-1865 (c)

Origin

England; London

Maker

Henry Barrow and Company

Class

magnetism; earth sciences

Earliest Date

1842

Latest Date

1865

Inscription Date

Material

metal (brass, silver, steel, tin); glass; wood; stone (agate); paper

Dimensions

box height 256mm; breadth 236mm; depth 173mm

Special Collection

Provenance

Purchased from Trevor Phillip & Sons Ltd., England, 09/1985.

Inscription

HENRY BARROW & Co, Mathematical & Optical Instrument Makers
‘HENRY BARROW & Co.
SUCCESSORS
TO THE LATE
T.C. Robinson from 38 Devonshire Street
Mathematical & Optical instrument makers.’ (trade label applied to inside of box)

Description Notes

Dip circle and accessories in a box, by Barrow, 1842-1865 (c).

Tribrach base, with three levelling screws, supporting horizontal circle divided 0-180 twice to 30’, read by vernier to 1’. Pivoted rectangular platform, with clamping screw, carrying bubble level and four pillars: two for needle mounting, two the vertical circle and microscopes. Needle mounting enclosed in removable glazed wooden box, with hinged door; needle axis carried in brass Y bearings and lowered onto agate edges by a knurled knob outside the box; two retaining arms for the axis also accessible from outside. Vertical circle with silver scale divided 1-180 twice to 30’, read by two silver verniers to 1’. Two adjustable reading microscopes, with reference wires (one broken) for the needle points; clamp and tangent screw; Lloyd’s attachment for external needle when measuring intensity. Three polished steel needles, steel axes fitted in brass, in tin boxes. Number “2” stamped on glazed box and storage box. Trade label (torn) applied to inside of box. One of two folded pieces of paper in a needle box contains a brass pin and carries a pencil note: ‘pin used by Ross’.

some pieces appear to be missing

References

Events

Description
A dip circle is used to measure the angle between the horizon and the earth’s magnetic field (the dip angle). They were used in surveying, mining and prospecting as well as for the demonstration and study of magnetism.

Georg Hartmann first discovered dip angle in 1544, when he noticed the needle on a compass dipped towards the north hemisphere. Rather than explore this phenomenon, Hartmann sought ways to eliminate it. However, Robert Norman investigated dip angle further and in 1581 described in print a device to measure this phenomena.

Early dip circles were not accurate and gave poor results. Over the next 300 years many improvements were made, including reducing the friction between the needle and its pivot and encasing the circle in glass. Initially, dip circles could only be used on land, but in 1834 Robert Were Fox designed the first that could be used on board a moving ship. This advance proved to be of major assistance to polar navigation, in particular in the discovery of the exact position of the South magnetic pole. Another important improvement to the instrument was developed in the 1830s by the Dublin Physicist Humphrey Lloyd, who devised a way of attaching a magnetic needle at right-angles to the dip needle in order to measure the intensity of force (by seeing the extent to which the right-angle needle deflected the dip-needle).

This instrument has Lloyd’s apparatus attached to the old pattern of square-framed apparatus. After the Arctic voyage of 1875-6 Lloyd’s apparatus was added to a version of the Fox round-framed dip circle. This, as produced by 1900, is known as the Lloyd-Creak dip circle.

The design of dip circles approached its peak at the beginning of the Twentieth century and by World War I the most advanced dip circles were being made. However, with the development of electronic systems dip circles became obsolete.
07/02/2008
Created by: Boris Jardine (with amendments by A. McConnell) on 07/02/2008

FM:39454