Robert Mallet Irish Engineer and Father of Controlled Source Seismology by: Thomas Blake, Geophysics Section, School of Cosmic Physics, DIAS

Transcription

1 Robert Mallet Irish Engineer and Father of Controlled Source Seismology by: Thomas Blake, Geophysics Section, School of Cosmic Physics, DIAS Many visitors to Dublin will be familiar with the large black cast iron railings that surround Trinity College and which are particularly visible along Nassau Street. Although many Dubliners pass by them several times a week, few, if any, take the time to read the name inscribed on the bottom of each of the main pillars, in some places becoming increasingly obscure by the many coatings of protective black paint applied over the years. In the places where the inscription is clear the letters J & R Mallet Trinity College Railings and Detail can be seen. This is the inscription of the father and son team John and Robert Mallet who operated the Victoria Foundry where the railings were manufactured in 1842 in Ryders Row, off Capel Street in Dublin and subsequently erected along Nassau Street. The place of Robert Mallet in the history of the advancement of science in Ireland has been neglected for many years and as we approach the bicentenary of his birth on June

2 3rd, 2010, we in DIAS hope to highlight his many achievements and indicate why they merit international recognition. Robert Mallet was born on June 3th Today a plaque in Ryders Row commemorates the place where Mallet lived and worked with his family. He graduated from Trinity College Ryders Row, Birthplace of R. Mallet Commemorative Plaque Dublin in 1830, with a BA degree having developed a strong interest in Mathematics and Science. After touring on the continent he joined his father s Victoria Foundry, then engaged on building many of the major bridges, railroads and other structural projects in Ireland. At the age of 22 Mallet was elected a member of the Royal Irish Academy and although metallurgy and corrosion were his main concerns, by 1842 his far-ranging interests were demonstrated by his election in 1836 to the newly founded Civil Engineers Society of Ireland, in 1838 to the Royal Society of Ireland and in 1839 as an Associate of the Institution of Civil Engineers, rising three years later to full membership. He was elected FRS in The publication of the first volume of Principles of Geology (1830) by Charles Lyell FRS ( ) was seized by Robert Mallet as a tool to further expand his growing fascination with geology and earthquakes. Mallet applied his knowledge of mechanics to the interpretation of Earth movements and their propagation a hitherto unexplored area of geology. The papers that Mallet read to the Royal Irish Academy between 1842 and 1846, published as On the dynamics of earthquakes are considered unique in their field. Mallet believed he was founding a true science of seismology a term first coined by him and first used in Mallet believed that the mathematical tools used by Sir William Rowan Hamilton FRS ( ) to describe the passage of light through crystals could also explain the passage of wave energy through rocks. Because large regular earthquakes do not occur in Ireland, therefore, to provide the energy needed for his seismic experiments Mallet had to resort to providing reliable alternative sources of energy. Mallet began to generate the large artificial shocks he needed for his experiments by detonating large controlled explosions. This was indeed a first in the world of science and remains the basis of controlled source seismological research since. He preformed his first controlled source experiments

3 Killiney Beach, Co Dublin in October and November of 1849 on Killiney Beach in south County Dublin. He was assisted by his eldest son, John and a small group of soldiers. The experiments consisted of exploding charges of 25lbs of gunpowder buried in the sands and measuring the travel time of the resultant shock wave at a distance of half a mile. The arrival of the resultant shock wave was recorded by the so called seismoscope invented also by Mallet. The results of the Killiney experiment yielded feet per second for shock waves in sand, less than that theoretically calculated by Mallet. So he decided to move the experiment onto solid rock to Dalkey Island in Here in the massive granite Mallet obtained results of ft per second compared to his calculated 8000ft per second. Puzzled by the discrepancy between his theoretical expectations and his observed experiments Mallet decide to plan an a large scale experiment in the quarries of Holyhead in Anglesey, Wales. This work was financed by the Royal Society and the British Association. The six Holyhead experiments were made between 1856 and 1861 using charges of gunpowder between 2,100 and 12,000 lbs and dislodging up to 36,000 of rock. The resultant speeds obtained for the shock waves and ft per sec were not too different from the previous Killiney and Dalkey experiments. Mallet concluded that his calculated theoretical speeds would never be achieved in reality. He knew enough about the properties of matter to believe that he was not observing compressional waves. He could be excused for not knowing what waves he had measured because it is likely that the waves were surface waves, probably Rayleigh waves. Rayleigh did not predict the existence of these waves until about forty years later. Mallet set out his research objectives in seismology in 1849 as follows: To experiment with the transmission of shock waves through the earth s crust To construct a self registering seismometer To compile a bibliography of seismological literature To produce a chronological catalogue of all of the earths known earthquakes To use the catalogue as the basis of the compilation of a map showing the global distribution of all earthquakes as known at that time.

4 Mallet s fascination with earthquakes and the dynamics of the earth resulted in the presentation of many papers of scientific interest to the Royal Irish Academy including ones such as On the dynamics of earthquakes (1846 and pub 1848). He presented papers also on topics such as an instrument to register shock waves in 1846.and also his Reports on the facts of earthquake phenomena in 1847, 1851, 1852 and On 16 December 1857 a very large earthquake, ranked then as the third most violent earthquake in human history devastated the area in South Italy not far from Salerno. On hearing the news Mallet applied for and received a grant from the Royal Society to enable him to study this event. There, he meticulously examined the area of devastation and photographed collapsed buildings and crevasses to enable him to determine the epicentre of the event. He also constructed for the first time a pioneering map using isoseismal lines to depict the varying severity of the shock experienced in the different parts of the devastated areas. This is the first time that photography, a relatively Pedrosa, South Italy, Devastation by the Great Neapolitan Earthquake of 1857 new invention was used as a significant scientific recording tool. The results of his detailed research into the earthquake appeared in 1862 in a magnificent and now classic two volume study offering a wealth of detailed observations and complete with a splendid array of dramatic illustrations. It is an irony that he is more widely know by school children in Southern Italy for his research efforts than he is in Ireland Robert Mallet is accredited by the Oxford Dictionary with coining the words seismology, seismoscope and isoseismal and other related words which he invented to describe his research. His contributions to seismology alone would even by today s standards leave many current researches rather envious. Their value is further enhanced when one

5 understands that he has also presented as many more significant research papers in the fields of material science, engineering and marine corrosion. By any objective measure the contribution of Robert Mallet to the advancement of science in Ireland and abroad is very impressive and significant. This is reflected in the honours awarded to him during his lifetime. On October 1832 he was elected a member of the Royal Irish Academy at the young age of 22, in May 1839 elected to an Associate of the Institution of Civil Engineers, elected in 1854 to the Fellowship of the Royal Society. On 15th March 1862 he received from the Royal Irish Academy its highest award The Cunningham Medal for his research in the theory of earthquakes. In 1862 he was awarded an honorary degree of Master of Engineering MAI by TCD and in 1864 he was awarded an honorary LL.D by the same university. On the 16 Feb 1877 he was awarded by the Geological Society of London, the world s oldest such organisation, its most prestigious prize the Wollaston Medal. As we approach the bicentenary of the birth of this very significant Irish scientist in June, 2010, we should be proud to acknowledge his great work and rejoice in the contribution that one young Irish Engineer from Ryders Row, off Capel Street in Dublin made in expanding the frontiers of science and his right to claim the title Father of Controlled Source Seismology. References COX, Ronald C Robert Mallet: Engineer and Scientist. In R. C. Cox (Editor), Robert Mallet , Centenary Seminar Papers, published by the Institution of Engineers of Ireland and the Royal Irish Academy, Ferrari, Graziano, McConnell Anita, Robert Mallet and the Great Neapolitan Earthquake of 1857 Notes Rec. R. Soc. 59(1), 25-64(2005) Herries Davies, G. L., Robert Mallet: Earth-scientist. In: R. C. Cox (Editor), Robert Mallet , Centenary Seminar Papers, published by the Institution Of Engineers of Ireland and the Royal Irish Academy,