physics

John Joly

John Joly is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand John Joly rather than just read about it. In short: John Joly (; 1 November 1857 – 8 December 1933) was an Irish geologist and physicist known for his development of radiotherapy in the treatment of cancer. In 1914, he worked with Walter Stevenson to establish the Irish Radium Institute, where they jointly developed the "Dublin method" for deep radiotherapy using hollow needles.

Key takeaways

John Joly belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect John Joly to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of John Joly from memory before moving on to harder problems.

Reference excerpt

John Joly (; 1 November 1857 – 8 December 1933) was an Irish geologist and physicist known for his development of radiotherapy in the treatment of cancer. In 1914, he worked with Walter Stevenson to establish the Irish Radium Institute, where they jointly developed the "Dublin method" for deep radiotherapy using hollow needles. He is also known for developing techniques to more accurately estimate the age of a geological period, based on radioactive elements present in minerals, the uranium–thorium dating.

Early life Joly was born in Holywood House (the Church of Ireland Rectory), Bracknagh, Kings's County, Ireland. He was a second cousin of astronomer Charles Jasper Joly. He entered Trinity College, Dublin in 1876, graduating in Engineering in 1882 in first place with several special certificates in branches of engineering, at the same time obtaining a First Class Honours in modern literature. He worked 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 held until his death in 1933 in Dublin. A keen yachtsman, he served as a Commissioner for Irish Lights.

Scientific career Joly joined the Royal Dublin Society in 1881 while still a student, and was a frequent contributor of papers. His first scientific paper was published in 1883, on the use of meteorological instruments at a distance. He published over 270 scientific papers. In 1886, Joly proposed a theory on the slipperiness of ice. According to Joly, when the ice is forced to contract by the pressure applied, a film of liquid water is formed, upon which actual slipping occurs. Although this theory has recently been superseded, it was the first time someone tried to explain the mechanism behind ice low friction. On 17 May 1899 Joly read his paper, "An Estimate of the Geological Age of the Earth", to the Royal Dublin Society. In it, he proposed to calculate the age of the Earth from the accumulation of sodium in the waters of the oceans. He calculated the rate at which the oceans should have accumulated sodium from erosion processes, and determined that the oceans were about 80 to 100 million years old. The paper was quickly published, appearing 4 months later in the Society's Scientific Transactions. Although this method was later considered inaccurate and was consequently superseded, it radically modified the results of other methods in use at the time. In 1903 he published an article in Nature in which he discussed the possibility of using radium to date the Earth and went on to study the radioactive content of the Earth's crust to formulate a theory of thermal cycles, and examined the radioactive constituents of certain rocks as a means of calculating their age. Working in collaboration with Sir Ernest Rutherford, he used 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 served as President of Section C (Geology) when the British Association for the Advancement of Science which met in Dublin in 1908, during which he presented his paper "Uranium and Geology" an address to the society. This work described 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 put forward the cohesion-tension theory which is now thought to be the main mechanism for the upward movement of water in plants. In 1914, he developed a method of extracting radium and applied it in the treatment of cancer. As a Governor of Dr Steevens' Hospital in Dublin, in collaboration with Walter Stevenson he devised radiotherapy methods and promoted the establishment by the Royal Dublin Society of the Irish Radium Institute where they pioneered the "Dublin method" of using a hollow needle for deep radiotherapy, a technique that later entered worldwide use. The Radium Institute also supplied capillary tubes containing radon to hospitals for some years for use in the treatment of tumours.

Inventions Joly invented a photometer for measuring light intensity, a meldometer for measuring the melting points of minerals, a differential steam calorimeter for measuring specific heats and a constant-volume gas thermometer, all of which bear his name, together with one of the first color photographic processes, the Joly colour screen. It was the first successful process for producing color images from a single photographic plate.

Awards and honours

Awards 1892: Fellowship of the Royal Society 1910: Royal Medal of the Royal Society 1911: Boyle Medal of the Royal Dublin Society 1923: Murchison Medal of the Geological Society of London

Honours After his death, his friends subscribed the sum of £1,700 to set up a memorial fund which is still used to promote the annual Joly Memorial Lectures at Trinity College Dublin, which were inaugurated by Ernest Rutherford in 1935. He is also remembered by the Joly Geological Society, a student geological association established in 1960. In 1930, Oliver Sheppard was commissioned by Trinity College Dublin and the Royal Dublin Society to make them copies of a bust of Joly. In 1973, Joly, an impact crater on Mars, was named in his honour.

Notes

References Jackson, Patrick Wyse (2006). The Chronologers' Quest: Episodes in the Search for the Age of the Earth. Cambridge University Press. ISBN 0-521-81332-8. "Joly, John" . Thom's Irish Who's Who . Dublin: Alexander Thom and Son Ltd. 1923. pp. 117-118 – via Wikisource.

External links The parrot, the pince-nez and the pleochroic halo at www.europhysicsnews.com Contribution of Offaly Writers to Irish Literature – Ancestral Research, Family History, Laois, Offaly, Genealogy at www.irishmidlandsancestry.com Works by John Joly at Project Gutenberg Works by or about John Joly at the Internet Archive

Illustrations

Worked examples

Example 1 — a first encounter with John Joly

Start with the simplest possible case. Write down what John Joly claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to John Joly before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about John Joly ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of John Joly

In research: John Joly appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses John Joly in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: John Joly is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1857 births, 1933 deaths, 19th-century Irish geologists, so understanding it makes those chapters shorter.
In everyday life: Look for John Joly outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study John Joly in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what John Joly means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain John Joly out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is John Joly in simple terms?

Why does John Joly matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study John Joly?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on John Joly.