Accession No
3123
Brief Description
dip circle, by H. Olland, Dutch, 1860 (c)
Origin
Netherlands; Utrecht
Maker
Olland, H.
Class
magnetism; earth sciences
Earliest Date
1860
Latest Date
1860
Inscription Date
Material
metal (brass, steel); glass; stone (agate); wood
Dimensions
box length 294mm; breadth 197mm; height 226mm
Special Collection
Provenance
Purchased from Tesseract, Hastings-on-Hudson, New York, USA. Purchased with the assistance of a grant from the Preservation Fund, Science Museum.
Inscription
‘H:OLLAND.
UTRECHT.’
Description Notes
dip circle, by H. Olland, 1860 (c).
Brass dip circle. Part glazed needle housing, clear glass at front (towards the vertical circle), removable ground glass plate at back. Two brass pillars carry agate supports. Y supports for raising needle, lever connection to screw outside housing. Bubble level. Vertical circle, divided on brass 0-90o-0-90o-0 to 30’, and by 2 versions to 1’. Clamp and tangent screws. 2 microscopes focus on ends of dip needle, 2 reading microscopes on jointed arm pivoted centrally with circle. Housing, circle and index arm pivot on horizontal circle, divided on brass 0-360o to 30’. Clamp and tangent screw. Tribach base, 3 knurled levelling screws. Wooden case. One metal-lined wooden box houses two steel dip needles. Second wooden box houses weighted support fitting needle suspension, with pivot for half-blued steel azimuth needle with jewel bearing; needle housing has two glazed side apertures with vertical reference lines for locating magnetic meridian. Wood and brass needle clamp fits on top of case, presumably for use when re-magnetising needles.
Condition: Fair (one reading microscope detached - solder broken)
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).
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:43041
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