In 1928, McCrea studies Albrecht Unsöld‘s hypothesis and discovers that three quarters of the sun is made of hydrogen and about one quarter is helium with 1% being other elements. Previous to this many people thought the sun consisted mostly of iron. After this, people realise most stars consist of hydrogen.
In 1932 McCrea moves to Imperial College London as a Reader and marries Marian Core the following year. In 1936 he becomes Professor of Mathematics and head of the mathematics department at the Queen’s University Belfast.
During World War II McCrea is co-opted onto the Admiralty Operational Research Group. After the war, he joins the mathematics department at Royal Holloway College in 1944. He is elected a Fellow of the Royal Society of London in 1952.
In 1964 McCrea proposes mass transfer mechanism as an explanation of blue straggler stars. In 1965, he creates the astronomy centre of the physics department at the University of Sussex.
John Joly, Irish physicist famous for his development of radiation therapy in the treatment of cancer, is born in Bracknagh, County Offaly, on November 1, 1857. He is also known for developing techniques to accurately estimate the age of a geological period, based on radioactive elements present in minerals.
Joly is a second cousin of Charles Jasper Joly, the astronomer. He enters Trinity College, Dublin in 1876, graduating in Engineering in 1882 in first place with various special certificates in branches of engineering, at the same time obtaining a First-Class Honours in modern literature. He works as a demonstrator in Trinity’s Engineering and Physics departments before succeeding William Johnson Sollas in the Chair of Geology and Mineralogy in 1897, a position which he holds until his death in 1933.
Joly joins the Royal Dublin Society in 1881 while still a student and is a frequent contributor of papers. During his career he writes over 270 books and scientific papers.
On May 17, 1899, Joly reads his paper “An Estimate of the Geological Age of the Earth” to the Royal Dublin Society. In it, he proposes to calculate the age of the earth from the accumulation of sodium in the waters of the oceans. He calculates the rate at which the oceans should have accumulated sodium from erosion processes and determines that the oceans are about 80 to 100 million years old. The paper is quickly published, appearing four months later in the Society’s Scientific Transactions. Although this method is later considered inaccurate and is consequently superseded, it radically modifies the results of other methods in use at the time.
In 1903 he publishes an article in Nature in which he discusses the possibility of using radium to date the Earth and goes on to study the radioactive content of the Earth’s crust to formulate a theory of thermal cycles and examines the radioactive constituents of certain rocks as a means of calculating their age. Working in collaboration with Sir Ernest Rutherford, he uses radioactive decay in minerals to estimate, in 1913, that the beginning of the Devonian period could not be less than 400 million years ago, an estimate which is in line with modern calculations.
Joly serves as President of Section C (Geology) when the British Association for the Advancement of Science meets in Dublin in 1908, during which he presents his paper “Uranium and Geology” in an address to the society. This work describes radioactive materials in rocks and their part in the generation of the Earth’s internal heat.
Along with his friend Henry Horatio Dixon, Joly also puts forward the cohesion-tension theory which is now thought to be the main mechanism for the upward movement of water in plants.
In 1914 Joly develops a method of extracting radium and applies it in the treatment of cancer. As a Governor of Dr. Steevens’ Hospital in Dublin, in collaboration with Walter Stevenson, he devises radiation therapy methods and promotes the establishment by the Royal Dublin Society of the Irish Radium Institute where they pioneer the “Dublin method” of using a hollow needle for deep radiation therapy, a technique that later enters worldwide use. The Radium Institute also supplies capillary tubes containing radon to hospitals for some years for use in the treatment of tumours.
Mallet is born in Dublin on June 3, 1810, the son of factory owner John Mallet. He is educated at Trinity College, Dublin, entering it at the age of 16 and graduating in science and mathematics in 1830 at the age of 20.
Following his graduation, he joins his father’s iron foundry business and helps build the firm into one of the most important engineering works in Ireland, supplying ironwork for railway companies, the Fastnet Rock lighthouse, and a swing bridge over the River Shannon at Athlone. He also helps manufacture the characteristic iron railings that surround Trinity College, and which bear his family name at the base.
In 1838 he becomes a life member of the Royal Geological Society of Ireland and serves as its President from 1846–1848. From 1848–1849 he constructs the Fastnet Rock lighthouse, southwest of Cape Clear.
On February 9, 1846, he presents to the Royal Irish Academy his paper On the Dynamics of Earthquakes, which is considered to be one of the foundations of modern seismology. He is also credited with coining the word “seismology” and other related words which he uses in his research. He also coins the term epicentre.
From 1852 to 1858, he is engaged in the preparation of his work, The Earthquake Catalogue of the British Association (1858) and carries out blasting experiments to determine the speed of seismic propagation in sand and solid rock.
On December 16, 1857, the area around Padula, Italy is devastated by the Great Neapolitan earthquake which causes 11,000 deaths. At the time it is the third largest known earthquake in the world and has been estimated to have been of magnitude 6.9 on the Richter Scale. Mallet, with letters of support from Charles Lyell and Charles Darwin, petitions the Royal Society of London and receives a grant of £150 to go to Padula and record at first hand the devastation. The resulting report is presented to the Royal Society as the Report on the Great Neapolitan Earthquake of 1857. It is a major scientific work and makes great use of the then new research tool of photography to record the devastation caused by the earthquake. In 1862, he publishes the Great Neapolitan Earthquake of 1857: The First Principles of Observational Seismology in two volumes. He brings forward evidence to show that the depth below the Earth’s surface, from where the impulse of the Neapolitan earthquake originated, is about 8–9 geographical miles.
One of Mallet’s papers is Volcanic Energy: An Attempt to develop its True Origin and Cosmical Relations, in which he seeks to show that volcanic heat may be attributed to the effects of crushing, contortion, and other disturbances in the crust of the earth. The disturbances leading to the formation of lines of fracture, more or less vertical, down which water would find its way, and if the temperature generated be sufficient volcanic eruptions of steam or lava would follow.
seamus dubhghaill 