Accession No
0510
Brief Description
dipleidoscope meridian instrument, by Edward John Dent, English, 1850 (c)
Origin
England; London
Maker
Dent, Edward John
Class
dials
Earliest Date
1843
Latest Date
1853
Inscription Date
Material
metal (brass, oxidozed brass, steel, white metal); glass; liquid
Dimensions
length 110mm; breadth 108mm; height 68mm
Special Collection
Robert Whipple collection
Provenance
Purchased from T.H. Court on 28/05/1927.
Inscription
‘E.J. DENT’S
PATENT
MERIDIAN INSTRUMENT.’’ (on cap for optical system)
82, Strand,
& 33, Cockspur St.
LONDON.’
Description Notes
Dipleidoscope meridian instrument, by E.J. Dent, English, c. 1850.
Square oxidized brass base on 1 foot and 2 levelling screws. 2 orthoganal bubble levels set on base. Also a glazed compass box with degree scale for magnetic variation divided [18˚] - 0 - [18˚] numbered by 5˚ subdivided to 1˚. Steel needle with brass locking mechanism operated from outside the box. Optical unit consists of 2 mirrors and clear glass cover set at an angle on base. Push-fit brass cover for optical unit.
Condition good (base chipped); complete
References
Events
Description
This instrument is used to determine true noon to an accuracy of within 10 seconds. A prism creates a double image of the sun, which merge together as the sun approaches its high point in the sky. When the two images overlap, it is local true noon.
The chronometer and clockmaker Edward John Dent patented his design for the dipleidoscope in 1843, and he exhibited the instrument at the Great Exhibition in London in 1851.
Knowing local noon is useful, for example, for checking and correcting clocks. It is also used in the determination of longitude, which can be calculated by finding the difference in time between local noon and midday at the prime meridian in Greenwich. Whilst the former can be found using a dipleidoscope or sextant, the latter must be read from an accurate chronometer set to Greenwich time.
16/07/2015
Created by: Joshua Nall on 16/07/2015
FM:39954
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