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Davies Gilbert (born Davies Giddy) (6 March 1767 – 24 December 1839) was a British engineer, author, and politician. He was elected to the Royal Society on November 17, 1791 and served as its President of the Royal Society from 1827 to 1830.
He was a close friend of Richard Trevithick and advised him on many of his inventions
The Dictionary of National Biography article says of him:
"Gilbert's importance to the development of science in the early nineteenth century lay in his faith that science provided the best means to tackle practical problems and in his facility as a parliamentary promoter of scientific ventures."
On 6 March 1767, he was born, the son of Edward Giddy, curate of St Erth church, and Catherine Davies, his wife, their only child. (He later changed his surname to "Gilbert").
He was educated at Penzance Grammar School and by his father
1789 June 29th. He graduated with an M.A. from Pembroke College, Oxford.
1792 Davies was High Sheriff of Cornwall from 1792 to 1793.
1804 He served in the House of Commons as Member of Parliament for Helston in Cornwall 1804-06 and for Bodmin from 1806-32.
He also had a great respect for the history and culture of Cornwall. For instance, he moved a Celtic cross from near Truro, on the Redruth Road (where it had found new use as a gatepost), to a place of respect in a Churchyard in his new home of Eastbourne.
1808 April 18th. He married Mary Ann Gilbert
1814 Gilbert was the President of the Royal Geological Society of Cornwall from its foundation in 1814 until his death in 1839.
1817 He took his wife's surname, Gilbert, to perpetuate it. This enabled the couple to inherit the extensive property in Sussex of her uncle who had no male heir.
1820 He was elected to the Society of Antiquaries in 1820.
1825 Davis(sic) Gilbert, 45 Bridge Street, Westminster, became a member of the Institution of Civil Engineers.
1826 He edited for publication a Cornish Language poem about the Passion: Pass yon Agna Alioth, as Mount Calvary (1826).
1837 He assembled and published 'A Parochial History of Cornwall' and collected and published a number of Cornish Carols.
Three daughters and a son survived him.
1840 Obituary 
It would be vain to expect that an Annual Meeting should ever recur without the Council having to lament the removal by death of some who, by their acquirements, or by their associations of friendship were endeared to the Institution.
The records of the Institution contain several communications from Mr. Logan, particularly one on the new Graving Dock at Dundee, and Mr. H. H. Price was, when in town, a constant attendant at the Meetings, and took a lively interest in the proceedings and success of the Institution.
Mr. Davies Gilbert was, by his writings and his influence, a great benefactor of practical science, and the transactions of the Royal Society, over which he presided for three years, contain several papers of great value to the practical engineer.
He took great interest in the introduction of Mr. Watt’s improvements in the steam engine into the Cornish mines, and in the controversy betwixt Mr. Watt and Mr. Jonathan Hornblower respecting working steam expansively, the former employing one cylinder only, the latter two cylinders, in the manner afterwards revived by Woolf; the theoretical efficiency of the two methods being identical, but simplicity and mechanical advantage being greatly in favour of the former, as its present universal adoption testifies.
Mr. Davies Gilbert introduced into practical mechanics the term 'efficiency' as the product of the applied force and of the space through which it acted in contradistinction to the term 'duty,' as indicative of a similar function of the work performed.
His attention was also directed to the theory of suspension bridges, when the plan for making such communication across the Menai was submitted to the Commissioners appointed by Parliament. It appeared to him that the proposed depth of curvature of the catenary was not sufficient, and his well-known theoretical investigation of this subject was undertaken with the view of ascertaining this fact; and in consequence of these investigations, the interval between the points of support of the chains and the road-way was increased to the height which appeared to him requisite for works of this nature.
The labours of this distinguished individual for the promotion of science were unremitting. He was the founder of several societies; he was the discoverer and early patron of the talents of Davy; and while in parliament he laboured most assiduously in the advancement of all the public works.
Regret for such a man, exerting the power of his mind so advantageously and through so many years, must always be strong and sincere; but having attained the ordinary limit of human life, he sunk into the grave amidst the respect and esteem of all who knew him, and has left behind him a name which will ever bear a prominent place amidst the names of those whose lives and talents have been devoted to great and noble purposes.