Shepherd Gate Clock
The Shepherd Gate Clock is a clock built into the right gate pillar of the entrance portal of the Royal Greenwich Observatory . The dial is attached to the outside, while the mechanism for driving the hands can be seen on the inside behind a glass front.
This clock is an early example of a public electric clock. The clock is a so-called slave clock that is controlled by a master clock. Slave clocks are only used to display the time and have no time-determining components such as pendulums or a balance wheel .
The Shepherd Gate Clock with the accompanying electrical clock system was designed in 1852 by Charles Shepherd jun. , an English chronometer maker , designed and installed. The clock system consisted of a master clock, three slave clocks inside the building and the so-called gate clock on the portal. The Gate Clock was the first clock that Greenwich Mean Time made available to the public. The 24-hour clock face is unusual for a public clock, but it was common for precision pendulum clocks in observatories.
History of the clock
The initiative to build the electrical clock system in Greenwich came from the Royal Astronomer Sir George Biddell Airy (* July 27, 1801, † January 2, 1892). With the advent of the railways, there was a need to have a single time nationwide. Many regions in England had a local time ( local time ) which sometimes differed considerably from one another. Airy suggested that a uniform time should be provided and disseminated from the Greenwich Observatory. He imagined that electricity could be used to send time signals to clocks (slave clocks) across the country, as well as to Europe and the British colonies. Another effect would be the possibility of precise measurements of the longitude for certain locations.
In 1849 Charles Shepherd jun. an electrical clock system in Pawson's Warehouse St. Paul's Churchyard London and in 1851 he received the order for an electrical clock system in the Crystal Palace exhibition building of the Great Exhibition in London's Hyde Park . Airy realized that Shepherd's electrical clock systems were suitable for realizing his idea of a unified time. On October 7, 1851, he wrote to Shepherd asking for an offer for an electrical clock system:
One automatic clock. One clock with large dial to be seen by the public, near the Observatory entrance, and three smaller clocks, all to be moved sympathetically with the automatic clock.
Airy also wished that the time ball that already existed in Greenwich should also be controlled by the clock system and thus slide down at exactly 13:00. With the help of the time ball, ships on the Thames were able to check their ship chronometers .
Shepherd responds promptly. He sent drawings and an offer to supply a master clock at £ 40 and slave clocks at £ 8 each. In the meantime, Airy had received the funds from the Admiralty and on December 19, 1851 gave Shepherd the contract to build and install the electrical clock system. In August 1852, Shepherd had installed the clock system in the observatory and put it into operation. On August 5, 1852, time signals from the Greenwich Observatory were sent to London for the first time.
The cost of the clock system turned out to be higher than originally estimated, totaling £ 224 (£ 70 for the master clock).
The master clock (Shepherd master clock) in the observatory was given different names over time, such as normal clock or master clock. The name Mean Solar Standard Clock later became common. Their main task was to generate second pulses that were needed to control the slave clocks. Slave clocks were installed in the Chronometer Room, Dwelling House (Flamsteed House) and at the gate. The pulses generated by the master clock were also transmitted via telegraph cable to London Bridge Station in London. From there different time signals were sent to all regions of England.
Airy describes the function of the Shepherd master clock in the Observatory's Board of Visitors from 1853:
Great progress had been made with the distribution of time. The same Normal Clock maintains in sympathetic movement the large clock at the entrance gate, two other clocks in the Observatory, and a clock at the London Bridge Terminus of the South-Eastern Railway. It sends galvanic signals every day along all the principal railways diverging from London. It drops the Greenwich Ball, and the Ball on the Offices of the Electric Telegraph Company in the Strand. All these various effects are produced without a sensitive error of time; and I cannot but feel a satisfaction in thinking that the Royal Observatory is thus quietly contributing to the punctuality of business through a large portion of this busy country.
Patent dispute with Bain
The gate clock bears the inscription: Shepherd Patentee 53 Leadenhall STt London Galvano Magnetic Clock. In 1852, Alexander Bain objected to the writing on the clock for patent infringement. After extensive correspondence with Bain's lawyer, Airy agreed to remove the lettering pending legal clarification. However, since this had not been done until 1853, the original lettering was reassembled.
Recent history
During the Second World War, the gate clock's face was so badly damaged that it had to be replaced.
The original Shepherd clock system is no longer functional. The Shepherd Gate Clock is now controlled by a modern pulse generator. The main clock (Shepherd master clock) as well as the other slave clocks can be seen in the clock exhibition of the observatory.
Individual evidence
- ↑ Autobiography of Sir George Biddell Airy, KCB, MA, LL.D., DCL, FRS, FRAS, Honorary Fellow of Trinity College, Cambridge, Astronomer Royal from 1836 to 1881. Edited by Wilfrid Airy, BA, M.Inst.CE 1896.
literature
- Howse, Derek (1997): Greenwich Time and the Longitude , Official Millennium ed., London: Philip Wilson, National Maritime Museum, ISBN 0-85667-468-0
- Chaldecott John A .: Platinum and the Greenwich System of Time-Signals in Britain. The Work of George Biddell Airy and Charles Vincent Walker from 1849 to 1870 By The Science Museum, London, in: Platinum Metals Rev., 1986, 30, (l), pp. 29-37.
- Douglas Bateman: The replacement of the war-damaged Shepherd dial at Greenwich by James Cooke & Son of Birmingham, in AHS No. 1, Vol. 36, pp. 84-90.
Web links
- National Maritime Museum : Slave clock and dial
- Watchmaker Biographies: Charles Shepherd