Mallet, Robert (1810–81), engineer and seismologist, was born 3 June 1810 in Ryder's Row, Dublin, eldest child and only son among three children of John Mallet (1780–1868), plumber, hydraulic-engine maker, and iron founder, and his wife and first cousin Thomasina Mallet (d. 1861). The Mallet family originated in Devon, and Robert's maternal grandfather, Robert Mallet sen. (1761–1804), came to Dublin and set up as a cabinet maker at 62 Capel St. He married Anne, daughter of William Pike, who had a plumbing business in Dublin since the 1750s. On Pike's death Robert sen. appeared to take over some of his father-in-law's business. After an invitation to his nephew in Devon, John Mallet came to join him, and married his daughter Thomasina. John also persuaded his father Richard Mallet to come to Dublin with his mother, brother, and sister. Richard Mallet set up business as an ironmonger at 90–91 Marlborough St., along with his other son, William. John took over the business on his uncle's death (1804), moving to premises at 7–9 Ryder's Row. He expanded the business and became involved in municipal affairs, acting as high sheriff of Dublin for a period.
Robert jun. showed an early interest in physical science and, as a youth, had a chemical laboratory fitted out for himself in his father's foundry. Educated at Bective House Seminary at 2 Denmark St., he entered Dublin University in December 1826. On graduating (1830) he joined his father's works at Ryder's Row, while receiving instruction in surveying and levelling from Joseph Byrne at 23 Lower Mount St. In 1831 he went on an extended tour of the Continent and visited the Mer de Glace at Chamonix, where he developed an interest in glacial flow. He later published a number of papers on the subject. The following year he became a full partner at his father's firm and developed it into one of the most important and successful engineering works in Ireland. At one stage his father built an extensive building on the banks of the Royal Canal near Phibsborough. Intended as a flour mill to be driven by a water wheel, it remained unused for several years because of problems in acquiring the water rights. The building was nicknamed ‘Mallet's folly’. The advent of the railway era led to large contracts for engineering and other works, and Robert converted the mill into a large factory with over forty smiths-fires, and planing and screwing machines. The firm built cast-iron bridges over the River Shannon, railway works for the Dublin–Kingstown and Great Southern & Western Railways, fire-engines for Dublin city, castings for the first Fastnet Lighthouse (1848–9) and the Nore viaduct, and contract work for Guinness & Co., TCD, Dublin Castle, the Records Office, and the Four Courts, among others. Developing his experimental skills further, Mallet researched extensively into the properties and strengths of various materials including alloys and the problems associated with the cooling of large iron castings, and was one of the first to carry out research on the corrosion of iron. He was one of the few iron-founders of the period to attempt a scientific explanation of fracture in terms of the ‘molecular strength’ of the metal. In 1834 he made his reputation as an engineer of exceptional skill by raising, by means of screw-jacks, the roof of St George's church in Dublin, for which he was later awarded the Walter premium from the Institution of Civil Engineers (1842). He invented and patented buckled plates (1852), which combined maximum strength with minimum depth and weight and were used to floor the Westminster and London bridges. During the Crimean war (1853–5) he began developing huge mortars for the war department, in the hope they would break the Russian hold on Sevastopol. The work was discontinued in 1858 after inconclusive tests and the cessation of hostilities.
Interest in scientific phenomena, particularly geological, was popular at the time, and Mallet took a keen interest in new developments. Using his knowledge of engineering and physics, and applying his skills of observation along with experimental measurement of natural phenomenon, he made several advances. He presented papers on magnetism and geology to the annual meetings of the British Association for the Advancement of Science in 1835 and 1837. In 1841 he surveyed the River Dodder, in an attempt to provide a steady water supply for the city and for a paper mill on its banks. During the same year he unsuccessfully applied for the chair of engineering at Dublin University. In February 1846 he read his classic paper ‘On the dynamics of earthquakes’ to the RIA, in which he proposed that the structural damage effected by earthquakes was caused by the action of ‘waves of elastic compression’ through the ground. He stressed the need for a quantified, experimental approach to the study of earthquakes. In October 1849 he conducted what were some of the first active seismic experiments – on the rate of shock waves in wet sand at Killiney beach. He buried gunpowder charges in the sand and measured the transit time of the resultant shock wave with a ‘seismoscope’, an instrument co-invented by Mallet and Thomas Romney Robinson (qv). He carried out similar experiments in the granite of Dalkey Island in October 1850. The Royal Society and the British Association commissioned more experiments at the government quarries in Holyhead between 1856 and 1861. Between 1852 and 1854 Mallet, with the cooperation of his son John William (qv), compiled a bibliography of seismological literature and a chronological catalogue of all the earth's known earthquakes, and published a seismographic map of the world, which noted the coincidence of seismic areas with volcanic activity. Through this published work he proposed and established the word ‘seismology’ for the study of earthquakes, and from this several new terms with the prefix ‘seism-’ were coined. He has been considered as the father of instrumental seismology.
In 1858 he was commissioned by the Royal Society to spend three months in Italy studying the after-effects of the great Neapolitan earthquake of December 1857. He examined the structural damage to buildings and crustal fixtures to determine the epicentre of the earthquake. His report was published as The great Neapolitan earthquake of 1857: the first principles of observational seismology (1862). During his stay in Italy, he developed an interest in volcanoes and he visited Vesuvius, Etna, and Stromboli in 1864, which formed the basis of his important paper ‘Volcanic energy’, which he read to the Royal Society (1873).
In 1860, owing to a shortage of contracts, he closed his business and relocated to London, where he set up offices at 11 Bride St. and later at 7 Westminster Chambers, and worked as a consultant engineer and writer. He edited (1861–7) the Practical Mechanic's Journal, contributed articles to the Engineer, and reported on the collieries of Westphalia. He was a prominent member of the scientific communities of Dublin and London and a member of the RIA (1832), Irish Society of Civil Engineers (1836), Institution of Civil Engineers (1842) (president 1866), Geological Society of Ireland (1838), the Geological Society of London (1859), an FRS (1864), and a member of the Institution of Mechanical Engineers (1867). He was the recipient of various honours and distinctions: an honorary degree from Dublin University (1864), the Cunningham medal from the RIA (1862), the Walker premium (1842), the Telford medal from the Institution of Civil Engineers (1859), and the Wollaston medal from the Geological Society of London (1877). He served as president of the Geological Society of Dublin (1846–8) and of the Institution of Civil Engineers of Ireland (1866).
A strongly independent spirit, Mallet stood apart from the fossil-loving geologists of his era. His inventive mind sought to find novel solutions to fresh problems in physical geology, and he always embraced the bigger picture. Somewhat overbearing, he frequently deprecated the efforts of others and seemed to view himself as above a general sea of mediocrity. On a personal basis he was a good friend and charming companion, which contradicted the supercilious tone he adopted in his writings. This may have been a defence against being seen as an outsider by the scientific community. He was, after all, an engineer and an amateur scientist among a community of professional scientists, academics, and gentlemen of science! He was proud of his native country and never neglected an opportunity to offer solutions to its problems, including the importation of technology to make it less dependent on agriculture. Left blind for the last seven years of his life, he became bedridden after an attack of diffuse cystitis in October 1880. He died 5 November 1881 at his home in Enmore, the Grove, Clapham Road, Surrey, and was buried in Norwood cemetery.
He married (November 1831) Cordelia Watson (d. 1854), daughter of a Dublin bookseller. In 1836 they moved from their home at Ryder's Row to Delville House in Glasnevin; they had three sons and three daughters. He later moved to 1 Grosvenor Terrace, Monkstown (1858). After moving to London in 1860 he married (1861) Mary Daniel, the daughter of the landlady of the house where he initially lodged on his arrival to London. They had no children. She and five of his children survived him. His three sons all engaged in careers in science or engineering: Dr John William Mallet (qv), chemist, of the University of Virginia, USA; Robert Trefusis Mallet, chief engineer of the Indian State Railways; and Frederick Richard Mallet (1840–1921), of the Geological Survey of India. A complete list of papers published by Robert Mallet between 1835 and 1880 can be found in R. C. Cox (ed.), Robert Mallet FRS 1810–1881 (1982), 135–9. The Mallet–Milne lectures, a series of public biennial lectures, have been established by the Society of Earthquake and Civil Engineering Dynamics at the Institute of Civil Engineers, London, in his honour.