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For other persons named John Michell, see John Michell (disambiguation). John Michell (1724–1793 was an English scientist John Michell may also refer to John Henry Michell (1863–1940 Australian mathematician

John Michell (December 25, 1724 – April 29, 1793) was an English natural philosopher and geologist, whose work spanned a wide range of subjects, from astronomy to geology, optics, and gravitation. Events 274 - Roman Emperor Aurelian Year 1724 ( MDCCXXIV) was a Leap year starting on Saturday (link will display the full calendar of the Gregorian calendar (or a Events 1429 - Joan of Arc arrives to relieve the Siege of Orleans. Year 1793 ( MDCCXCIII) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian calendar (or a Common England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland A geologist is a contributor to the Science of Geology, studying the physical structure and processes of the Earth and planets of the solar system Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study Geology (from Greek γη gê, "earth" and λόγος Logos, "speech" lit Gravitation is a natural Phenomenon by which objects with Mass attract one another He was both a theorist and an experimenter. The word theory has many distinct meanings in different fields of Knowledge, depending on their methodologies and the context of discussion. In scientific inquiry an experiment ( Latin: Ex- periri, "to try out" is a method of investigating particular types of research questions or

Michell was educated at Queens' College, Cambridge and later became a Fellow of Queens'. Queens' College is a constituent college of the University of Cambridge. He obtained his M. A. in 1752, and B. D. in 1761. In 1760 he was elected a Fellow of the Royal Society, in the same year as Henry Cavendish. Year 1760 ( MDCCLX) was a Leap year starting on Tuesday (link will display the full calendar of the Gregorian calendar (or a Leap The Royal Society of London for the Improvement of Natural Knowledge, known simply as The Royal Society, is a Learned society for science that was founded in 1660 Henry Cavendish, FRS (10 October 1731 - 24 February 1810 was a British Scientist noted for his discovery of Hydrogen or what he called "inflammable In 1762 he was appointed Woodwardian Professor of Geology, and in 1767 he became rector of Thornhill, West Yorkshire, near Dewsbury, where he died. Year 1762 ( MDCCLXII) was a Common year starting on Friday (link will display the full calendar of the Gregorian calendar (or a Common year The Woodwardian Professor of Geology is a professorship at the University of Cambridge. Thornhill, is a village in West Yorkshire, England. It is located on a hill on the south side of the River Calder, and has extensive views of Dewsbury Dewsbury is a Market town within the Metropolitan Borough of Kirklees, in West Yorkshire, England.

He was thus described by a contemporary commentator:

John Michell, BD is a little short Man, of a black Complexion, and fat; but having no Acquaintance with him, can say little of him. I think he had the care of St. Botolph’s Church Cambridge, while he continued Fellow of Queen's College, where he was esteemed a very ingenious Man, and an excellent Philosopher. The city of Cambridge (ˈkeɪmbrɪdʒ is a university town and the administrative centre of the county of Cambridgeshire, England He has published some things in that way, on the Magnet and Electricity. In Physics, magnetism is one of the Phenomena by which Materials exert attractive or repulsive Forces on other Materials. ’

(Cole MSS XXXIII, 156, British Library).

Contents

Work

Gravity, magnetism & light

Michell conceived, sometime before 1783, the experiment now known as the Cavendish experiment. The Cavendish experiment, done in 1797 &ndash 1798 by Henry Cavendish, was the first experiment to measure the force of gravity between masses in the laboratory It was the first to measure the force of gravity between masses in the laboratory, and produced the first accurate values for the mass of the Earth and the gravitational constant. Gravitation is a natural Phenomenon by which objects with Mass attract one another The gravitational constant, denoted G, is a Physical constant involved in the calculation of the gravitational attraction between objects with mass He invented and built, independently of co-inventor Charles Augustin de Coulomb, a torsion balance for the experiment, but didn’t live to put it to use. Charles Augustin de Cock (June 14 1736 Angoulême France – August 23 1806 Penis France was a French Physicist. A torsion spring is a spring that works by torsion or twisting that is a flexible elastic object that stores Mechanical energy when it is twisted His apparatus passed to Henry Cavendish who performed the experiment in 1798. Henry Cavendish, FRS (10 October 1731 - 24 February 1810 was a British Scientist noted for his discovery of Hydrogen or what he called "inflammable In 1987, gravity researcher A. H. Cook wrote:

The most important advance in experiments on gravitation and other delicate measurements was the introduction of the torsion balance by Michell and its use by Cavendish. It has been the basis of all the most significant experiments on gravitation ever since. [1]

In 1750 he published at Cambridge a work of some eighty pages entitled A Treatise of Artificial Magnets, in which is shown an easy and expeditious method of making them superior to the best natural ones. Year 1750 ( MDCCL) was a Common year starting on Thursday (link will display the full calendar of the Gregorian calendar (or a Besides the description of the method of magnetization which still bears his name, this work contains a variety of accurate magnetic observations, and is distinguished by a lucid exposition of the nature of magnetic induction. Faraday's law of induction describes an important basic law of electromagnetism which is involved in the working of Transformers Inductors and many forms of

At one point, Michell attempted to measure the radiation pressure of light by focusing sunlight onto one side of a compass needle. Radiation pressure is the Pressure exerted upon any surface exposed to Electromagnetic radiation. The experiment was not a success: the needle melted.

Geology

In scientific biographies written during the early 20th century, Michell's historical importance is ascribed to his work on geology. The twentieth century of the Common Era began on His most important geological essay was entitled "Conjectures concerning the Cause and Observations upon the Phaenomena of Earthquakes" (Philosophical Transactions, li. The Philosophical Transactions of the Royal Society, or Phil Trans 1760), which showed a remarkable knowledge of the strata in various parts of England and abroad. Year 1760 ( MDCCLX) was a Leap year starting on Tuesday (link will display the full calendar of the Gregorian calendar (or a Leap

Effect of gravity on light

More recently, Michell's main "claim to fame" is considered to be his letter to Cavendish, published in 1784, on the effect of gravity on light. This paper was only generally "rediscovered" in the 1970s and is now recognised as anticipating several astronomical ideas that had been considered to be 20th century innovations. Michell is now credited with being the first to study the case of a heavenly object massive enough to prevent light from escaping (the concept of escape velocity was well known at the time). In Physics, escape velocity is the speed where the Kinetic energy of an object is equal to the magnitude of its Gravitational potential energy Such an object would not be directly visible, but could be identified by the motions of a companion star if it was part of a binary system. Michell also suggested using a prism to measure the gravitational weakening of starlight due to the surface gravity of the source ("gravitational shift"). In Optics, a prism is a transparent optical element with flat polished surfaces that refract Light. In Physics, Light or other forms of Electromagnetic radiation of a certain wavelength originating from a source placed in a region of stronger gravitational Michell acknowledged that some of these ideas were not technically practical at the time, but wrote that he hoped they would be useful to future generations. By the time that Michell's paper was "resurrected" nearly two centuries later, these ideas had been reinvented by others.

The mathematician Pierre-Simon Laplace suggested the same idea of high-gravity objects trapping light in his book Exposition du Systeme du Monde in 1796. Year 1796 ( MDCCXCVI) was a Leap year starting on Friday (link will display the full calendar of the Gregorian calendar (or a Leap year This sort of high-gravity object under Newtonian theory is commonly referred to as a dark star, and can be thought of as being the predecessor of the modern idea of a black hole under general relativity. A dark star is a theoretical object compatible with Newtonian mechanics that due to its large mass has a surface Escape velocity that equals or exceeds the A black hole is a theoretical region of space in which the Gravitational field is so powerful that nothing not even Electromagnetic radiation (e General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916

Some of Michell's contributions

External links

References

  1. ^ Cook, A. H. (1987), “Experiments in Gravitation”, in Hawking, S. W. and Israel, W. , Three Hundred Years of Gravitation, Cambridge University Press, pp. p. 52, ISBN 0521343127 


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