Trigonometric survey of Great Britain and Ireland

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Triangulation Network of Great Britain and Ireland 1860

The Trigonometric Survey of Great Britain and Ireland ( English Principal Triangulation of Great Britain ), which followed the Anglo-French Trigonometric Survey from 1784 to 1790 and lasted from 1791 to 1853, was the first triangulation of the whole of Great Britain and Ireland . It was through them that the Ordnance Survey began .

The story of this survey began by accident. Charles Lennox, 3rd Duke of Richmond , from 1784 to 1795 Master-General of the Ordnance , was able to acquire the theodolite in 1791 , which Jesse Ramsden had built for the East India Company , but which was not accepted by the East India Company . According to the information provided by William Roy, it was an improved version of the theodolite that he had received in 1787 for the English-French trigonometric measurement. In addition, two 30 m (100 ft) long measuring chains, also made by Ramsden, were acquired. The date of purchase, June 21, 1791, has been the founding date of the Ordnance Survey ever since. Immediately afterwards, William Mudge, Isaac Dalby and Edward Williams were commissioned by the Duke of Richmond to do the survey. In its early years, the Ordnance Survey was housed at the headquarters of the Board of Ordnance in the Tower of London .

First, the baseline at Hounslow Heath was measured again with one of the chains, while the second was kept for comparison purposes. The ends of the baseline were permanently secured with two cannon barrels sunk into the ground,

The triangulation then initially moved along the south coast, about which precise information was urgently needed in view of the feared French invasion. In the summer of 1794 another baseline was measured with the chain at Salisbury .

Land's End was reached in 1795 . The locations of Lizard Point and the Isles of Scilly were determined the following year. The south-east of England was measured in detail with another, slightly smaller theodolite built by Ramsden. In this way they worked their way further north over the years. A meridian arc from the Isle of Wight to Yorkshire was also measured. In Oxfordshire they compared their own observations with those made by George Spencer, 4th Duke of Marlborough in his observatory at Blenheim Palace with his quadrant , also built by Ramsden . The meridian arc was later extended to the Shetland Islands .

In later years Thomas Frederick Colby , who was Superintendent of the Survey for 27 years, extended the network to Scotland and Ireland. He died shortly before the final report was completed.

The Ordnance Survey Drawings were produced on the basis of this network . Before the detailed maps could be published, the correct names of the places and rivers first had to be determined and recorded in long lists, which was not easy in the country with often different pronunciation. The original drawings of the maps of Endland and Wales are now in the British Library .

literature

Individual evidence

  1. ↑ The Kingdom of Great Britain and the Kingdom of Ireland were ruled in personal union until 1800. The Act of Union passed by both parliaments in 1801 made it the United Kingdom of Great Britain and Ireland , which existed until 1927.
  2. ↑ Jane Insley: The Tale of the Great Theodolites on fig.net, the website of the International Federation of Surveyors
  3. ^ Ordnance Survey history on ordnancesurvey.co.uk
  4. ↑ It is believed that the cannon barrels at Heathrow on the corner of Northern Perimeter Road-Nene Road ( ) and in Hampton on Roy Grove ( ) are no longer exactly in place today as a result of various construction works.World iconWorld icon
  5. ^ William Mudge: Account of the Measurement of an Arc of the Meridian from Dunnose, Isle of Wight, to Clifton in Yorkshire. P. 485
  6. ↑ Ordnance Survey drawings on bl.uk