Sir Charles Edward Inglis (; 31 July 1875 – 19 April 1952) was a British civil engineer. The son of a medical doctor, he was educated at Cheltenham College and won a scholarship to King's College, Cambridge, where he would later forge a career as an academic. Inglis spent a two-year period with the engineering firm run by John Wolfe-Barry before he returned to King's College as a lecturer. Working with Professors James Alfred Ewing and Bertram Hopkinson, he made several important studies into the effects of vibration on structures and defects on the strength of plate steel.
Inglis served in the Royal Engineers during the First World War and invented the Inglis Bridge, a reusable steel bridging system – the precursor to the more famous Bailey bridge of the Second World War. In 1916 he was placed in charge of bridge design and supply at the War Office and, with Giffard Le Quesne Martel, pioneered the use of temporary bridges with tanks. Inglis retired from military service in 1919 and was appointed an Officer of the Order of the British Empire. He returned to Cambridge University after the war as a professor and head of the Engineering Department. Under his leadership, the department became the largest in the university and one of the best regarded engineering schools in the world. Inglis retired from the department in 1943.
Inglis was associated with the Institution of Naval Architects, Institution of Civil Engineers, Institution of Mechanical Engineers, Institution of Structural Engineers, Institution of Waterworks Engineers and British Waterworks Association; he sat on several of their councils and was elected the Institution of Civil Engineers' president for the 1941–42 session. He was also a fellow of the Royal Society. Inglis sat on the board of inquiry investigating the loss of the airship R101 in 1930 and was chair of a Ministry of War Transport railway modernisation committee in 1946. Knighted in 1945, he spent his later years developing his theories on the education of engineers and wrote a textbook on applied mechanics. He has been described as the greatest teacher of engineering of his time and has a building named in his honour at Cambridge University.
Early life and career Charles Inglis was the second son of Dr. Alexander Inglis (a general practitioner in Worcester) and his first wife, Florence, the daughter of newspaper proprietor John Frederick Feeney. His elder brother was the historian John Alexander Inglis FRSE Their father, Alexander Inglis was born in Scotland to a respectable family – his grandfather, John Inglis, was an Admiral in the Royal Navy and had captained HMS Belliqueux at the Battle of Camperdown in 1797.
Charles Inglis was born on 31 July 1875. He was not expected to survive and was hurriedly baptised in his father's drawing room; his mother died from complications eleven days later. His family moved to Cheltenham and Inglis was schooled at Cheltenham College from 1889 to 1894. In his final year, he was elected head boy and received a scholarship to study the Mathematics Tripos at King's College, Cambridge. Inglis was 22nd wrangler when he received his Bachelor of Arts degree in 1897; he remained for a fourth year, achieving first class honours in Mechanical Sciences. Inglis was a keen sportsman and enjoyed long-distance running, walking, mountaineering and sailing. At Cambridge, he nearly achieved a blue for long-distance running but was forced to withdraw from a significant race because of a pulled muscle. He was also a follower of the Cambridge University Rugby Union team, watching their matches at Grange Road.
After graduation, Inglis began work as an apprentice for the civil engineering firm of John Wolfe-Barry & Partners. He worked as a draughtsman in the drawing office for several months before being placed with Alexander Gibb, who was acting as resident engineer on an extension to the Metropolitan District Railway between Whitechapel and Bow. Inglis was responsible for the design and supervision of all thirteen bridges on the route. It was during this time that he began his lifelong study of vibration and its effects on materials, particularly bridges.
Early academic career In 1901 Inglis was made a fellow of King's College after writing a thesis entitled The Balancing of Engines, the first general treatment of the subject – which was becoming increasingly important due to the growing speeds of locomotives. In the same year, he received his Master of Arts degree and was accepted as an Institution of Civil Engineers (ICE) associate member after winning the institution's Miller Prize for his student paper on The Geometrical Methods in Investigating Mechanical Problems. Inglis left his employment with Wolfe-Barry, having completed two years of his five-year apprenticeship, to return to King's College and become an assistant to James Alfred Ewing, professor of mechanism and applied mechanics. Inglis maintained his interest in engine balancing and filed a US patent on 16 April 1902 for an improved engine with the cylinders mounted end to end to balance out the forces acting between them.
Professor Ewing left the university in 1903 to become the first Director of Naval Education at the Admiralty but Inglis remained; he was appointed a university demonstrator in mechanism by Professor Bertram Hopkinson, Ewing's successor, and worked with him to study the effects of vibration. Inglis was promoted to lecturer of mechanical engineering in 1908. Hopkinson recognised Inglis's academic abilities and assigned him the heaviest teaching load of all the staff, covering statics, dynamics, structural engineering theory, materials engineering, drawing, engine balance and the design of steel girders and reinforced concrete. Inglis later recalled that if he wished to learn more on a subject then he volunteered to teach a course on it. From 1911 Inglis became involved in hydraulic engineering and served on the board of the Cambridge University and Town Waterworks Company, serving as deputy chairman from 1924 to 1928 and chairman from 1928 to 1952.
Inglis conducted research into the problem of fracture in the metal plates of ships' hulls and noticed that the rivet holes along the path of a crack were often deformed into an elliptical shape. This phenomenon led him to investigate the magnification of stress caused at the edges of an elliptical defect; in 1913 he published a paper of his theories that has been described as his most important contribution to engineering and the first serious modern work on the fracturing of materials. Alan Arnold Griffith later drew on Inglis's paper for his work on the apparent discrepancy between calculated and actual strengths of materials. Inglis's 1913 paper has been cited by around 1,200 subsequent works.
Inglis had married Eleanor Moffat, daughter of Lieutenant-Colonel Herbert Moffat of the South Wales Borderers, in 1901, having met on holiday in Switzerland. They lived at Maitland House, Cambridge, until 1904, when Inglis built a house he named Balls Grove at nearby Grantchester, where his two daughters were born and the family resided until 1925. They later moved to 10 Latham Road, which Inglis renamed Niddrys after the first known address of his ancestors in Edinburgh.
Military service
Inglis was involved with the Cambridge University Officer Training Corps (CUOTC), being commissioned a second lieutenant on 24 May 1909. He served with the CUOTC's engineering detachment and noticed that when the unit was deployed on field days with the rest of the force it often had little to do. To remedy this, Inglis designed a reusable steel bridge, with the intention that it could be erected and dismantled by the unit in a single afternoon. An army general who was inspecting the unit noticed his design and offered advice: "If you're making anything for the army, keep it simple – no complicated gadgets". Upon the outbreak of the First World War in 1914, Inglis volunteered for active service in the British Army and was officially listed as an Assistant Instructor in the School of Military Engineering, with the temporary rank of lieutenant. The army expressed interest in Inglis's bridge design; it was approved for use by a panel of army officers that included the general who had first commented on the design, to whom Inglis said "I hope, Sir, you will find I have profited by your advice". The design remained in service with the British Army until the higher-capacity Bailey bridge was introduced during the Second World War.
The Inglis Bridge was designed so that all of its components could be moved by manpower alone; moreover, it could be erected with few tools in a short span of time – a troop of 40 sappers could erect a bridge in 12 hours. The design was composed of a series of Warren truss bays made from tubular steel sections, to a maximum span of six bays (). The design went through three revisions, with the Mark II replacing the original design's variable-length tubes with identical-length ones and, during the Second World War, the Mark III using higher strength steel but smaller tube diameters, increasing the carrying capacity to . In addition to his bridge design, during the war's course he developed the similar Inglis Tubular Observation Tower. Inglis received a US Patent for his bridge on 25 April 1916 and for the type of joints used in it on 26 June 1917.
In 1916, Inglis was placed in charge of bridge design and supply at the War Office in which role he was a proponent for the increased use of girder bridges in military applications. It was Inglis that first proved to the army that the heavy components essential to girder bridges did not prevent their rapid assembly in field conditions. This led to the greater use of such bridges, particularly the Inglis Bridge, for tanks later in the war. He received promotion to the rank of captain on the General List of Officers on 6 May 1916 and became a staff captain attached to the War Office on 26 June 1917. He was promoted to the brevet rank of major as part of the King's Birthday Honours on 3 June 1918 and later that year worked with Giffard Le Quesne Martel to develop some of the earliest bridgelaying tanks. Inglis retired from the army on 9 March 1919, having been rewarded for his military service with an appointment as an Officer of the Order of the British Empire.
Return to King's College
Inglis returned to Cambridge in 1918 and was appointed as the professor of Mechanism and Applied Mechanics (renamed Mechanical Sciences in 1934). On 25 March 1919, he was selected to head the Cambridge University Engineering Department as the successor of Hopkinson, who had died in an air crash the previous year. Though he made no radical changes, such as had occurred under his predecessors, under Inglis's supervision the department became the largest in the university and one of the best engineering schools in the world. He was responsible for expanding the department to meet the increased post-war demand for engineers and for the move from its traditional home at Free School Lane. Inglis acquired the Scroope House on Trumpington Street for the department and constructed a laboratory on the site by 1923, followed in 1931 by a structure containing lecture theatres and a drawing office.