Dipleidoscope A dipleidoscope is an instrument used to determine true

noon Noon (or midday) is 12 o'clock in the daytime. It is written as 12 noon, 12:00 m. (for meridiem, literally 12:00 noon), 12 p.m. (for post meridiem, literally "after noon"), 12 pm, or 12:00 (using a 24-hour clock) or 1200 ( military time). Sola ...

; its name comes from the Greek for ''double image viewer''. It consists of a small

telescope A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to observ ...

and a

prism Prism usually refers to: * Prism (optics), a transparent optical component with flat surfaces that refract light * Prism (geometry), a kind of polyhedron Prism may also refer to: Science and mathematics * Prism (geology), a type of sedimentary ...

that creates a double image of the sun. When the two images overlap, it is local true noon. The instrument is capable of determining true noon to within ten seconds. The dipleidoscope was invented by

Giovanni Battista Amici Giovanni Battista Amici (; 25 March 1786 – 10 April 1863) was an Italian astronomer, microscopist, and botanist. Amici was born in Modena, in present-day Italy. After studying at Bologna, he became professor of mathematics at Modena, and in 18 ...

in the first half of the 19th century.

Edward John Dent Edward John Dent (1790–1853) was a famous English watchmaker noted for his highly accurate clocks and marine chronometers. He founded the Dent company. Early years Edward John Dent, son of John and Elizabeth Dent, was born in London on 1 ...

, a chronometer and clockmaker in London, was working in the 1830s on a simple contrivance that would allow the public to set clocks correctly based on the transit of the sun (more complex and expensive transit telescopes had been developed by Ole Rømer in 1690). By 1840 he felt he had come to a suitable design using shadows, however when he communicated his ideas to Mr J.M. Bloxam (a barrister), he found he had also been working on his own design using reflections, which Dent felt was superior. The two formed a partnership and worked together on the device, and after a further 2 years work they finalised the design and patented it (GB Patent 9793 of 1843), with Mr Dent manufacturing and selling it as Dent's Dipleidoscope.'Dent's Dipleidoscope, or transit instrument for the correction of time-keepers', The Practical Mechanic and Engineer's Magazine, Jan 1845, pp100-101 The instrument could use the moon as well as the sun and when correctly calibrated and aligned the accuracy was said to be less than a second. Dent exhibited the device at the Great Exhibition of 1851. After Edward Dent died in 1853, his son Frederick William Dent took over manufacture. The significance of this device relates in part to the development of the railways, when an absolute knowledge of the time became more important, whereas previously it was often sufficient that an entire rural community would use the parish clock, and this would periodically be set by 'the announcement of the guard of the mail coach' or similar. The instrument came with a detailed instruction booklet, which had a substantial section on correcting local time to Greenwich Mean time (as used by the railways).

References

External links

A dipleidoscope of the National Observatory of Athens
Optical instruments Clocks Italian inventions {{optics-stub