96th Auction
2017/11/18
Lot 282
E. J. Dent, 82 Strand & 33 Cockspur Street, London, Case No. 472, 77 mm, circa 1845
A rare meridian instrument 'Dipleidoscope' according to Dent's patent of 1843
Case: brass.
The importance of this peculiar little instrument in the mid 19th century is considerable. At the time - without reliable portable watches and modern means of communication - it was near impossible to regulate chronometers or to test a precision clock. Away from the visual range of the famous time ball at Greenwich, people used relatively accurate regulators that were adjusted at regular intervals, or even - as described by Cedric Jagger in the introduction of his book on Paul Philip Barraud - "time couriers": employees of the chronometer makers who brought the correct time with them from a trip to Greenwich. Another method was using the position of the sun (which was sometimes difficult in England) to determine the true noon to find the exact mean time with the equation table.
The instrument was developed by E. J. Dent (1790-1853) and his partner J. M. Bloxam and promised to be a simple method to determine true noon. The outer glass panel and the two mirrors behind it create a hollow prism that is aligned in parallel to the axis of the Earth. When the instrument is set up correctly, a double image of the sun is created on the glass panel as well as on the inner mirrors. When the angle of the mirrors coincides with the angle of the sunlight, the two images overlap and it is local true noon. The instrument is said to be capable of determining true noon to within a few seconds.
In his 25 page paper "Dent on the Dipleidoscope - with Instructions for its Use and Fixing" dating from 1845, Dent himself describes his instrument. Illustrations show English gentlemen using the dipleidoscope with their pocket watches on the stairs of their country house or using the device on the windowsill of their house. The appendix of Dent’s booklet contains the equation table.
The company Dent produced their meridian instruments up to the turn of century and as late as 1907, a watchmaker’s guide recommended the practical use of the dipleidoscope.
The way this instrument was finished indicates that it is a somewhat upmarket version: the base that supports the prism has been decorated with volute ornaments, which is unusual and much more time-consuming to make than the standard version as shown in Dent’s paper.
A rare meridian instrument 'Dipleidoscope' according to Dent's patent of 1843
Case: brass.
The importance of this peculiar little instrument in the mid 19th century is considerable. At the time - without reliable portable watches and modern means of communication - it was near impossible to regulate chronometers or to test a precision clock. Away from the visual range of the famous time ball at Greenwich, people used relatively accurate regulators that were adjusted at regular intervals, or even - as described by Cedric Jagger in the introduction of his book on Paul Philip Barraud - "time couriers": employees of the chronometer makers who brought the correct time with them from a trip to Greenwich. Another method was using the position of the sun (which was sometimes difficult in England) to determine the true noon to find the exact mean time with the equation table.
The instrument was developed by E. J. Dent (1790-1853) and his partner J. M. Bloxam and promised to be a simple method to determine true noon. The outer glass panel and the two mirrors behind it create a hollow prism that is aligned in parallel to the axis of the Earth. When the instrument is set up correctly, a double image of the sun is created on the glass panel as well as on the inner mirrors. When the angle of the mirrors coincides with the angle of the sunlight, the two images overlap and it is local true noon. The instrument is said to be capable of determining true noon to within a few seconds.
In his 25 page paper "Dent on the Dipleidoscope - with Instructions for its Use and Fixing" dating from 1845, Dent himself describes his instrument. Illustrations show English gentlemen using the dipleidoscope with their pocket watches on the stairs of their country house or using the device on the windowsill of their house. The appendix of Dent’s booklet contains the equation table.
The company Dent produced their meridian instruments up to the turn of century and as late as 1907, a watchmaker’s guide recommended the practical use of the dipleidoscope.
The way this instrument was finished indicates that it is a somewhat upmarket version: the base that supports the prism has been decorated with volute ornaments, which is unusual and much more time-consuming to make than the standard version as shown in Dent’s paper.
Sold
estimated
2.000—3.000 €
Price realized
1.800 €