John Michel

John Michel (or Mitchell , 1724 - April 29th 1793) is a physicist, astronomer and British geologist . Some of its work were redécouverts by the astronomers only in the years 1970. He is regarded as one of the founders of modern seismology, because it was the first to suggest that the movements of the ground implied in an earthquake were propagated inside the Earth in the form of waves starting from a rupture in the Earth's crust. This idea had come to him after the great seism from Lisbon, which took place in 1755 and which plays a big role in the novel Candide of Voltaire. It also seems that John Michel was the first to imagine an enough heavy celestial object to prevent any exhaust of light; this idea did not have anything mysterious for the time, since the concept of Escape velocity was well-known since Newton and that this last considered the light in the form of corpuscles moving at the given speed in 1675 with the Observatoire of Paris by the Danish astronomer Olaf Rømer. Such an object would be then invisible. It is what one calls today a Black hole. Thus, Michel preceded the mathematician Pierre-Simon Laplace who promoted to him also the same idea in his book Exposition of the System of the World in 1796.

Michel followed his schooling to the Queens College to Cambridge. He obtained his M.A. in 1752, and his STRIP CARTOONS in 1761. He was named professor of geology in 1762, and 1767 vice-chancellor of Thornhill in the Yorkshire, where he will die. He was elected member of the Royal Society the same year as Henry Cavendish (1760). In 1750, it published a text of approximately eighty pages on the Aimant S ( has Treatise Artificial Magnets off), in which it provides a simple method to increase the intensity of Aimantation. In addition to the description of this method which bears the name of “method of Michel”, the text in question contains also several precise observations on the Magnétisme, and in particular on the magnetic phenomenon of Induction. Michel was the inventor of the Balance of torsion become famous thanks to the applications that made Henry Cavendish of it to determine the Masse of the Earth and Charles-Augustin of Coulomb to draw up the fundamental law of electrostatics (“law of Coulomb”). By building his torsion balance, Michel proposed to determine the Constante gravitation of Newton G and, like the constant GM was known by the third law of Kepler or measurements of the period of oscillation of a pendulum, to draw the mass M from it from the Earth and thus also his average density . Michel died before being able to use his device in practice. The balance of Michel passed first of all to Wollaston (the inventor of the goniometer which bears its name) which, too undoubtedly occupied by its crystallographic research, did not do anything separately of it to transmit it to Cavendish. This last improved the apparatus very slightly and could thus determine in 1798 the constant of gravitation, and thus the mass of the Earth, with a reasonable precision. The name of Sir Henry Cavendish remained attached to this very famous experiment which was reproduced many times while benefitting from technical projections. However, to return in César what returns in César, one should rather speak about the “experiment about Michel and Cavendish”.

Some of its other contributions:

Conjectures concerning the Cause and Observations upon the Phaenomena off Earthquakes Philosophical Transactions
Observations One the off Makes January 1760 At Cambridge , Philosophical Transactions (1760)
has off Recommendation Hadley' S Quadrant for Surveying , ibid (1765)
Proposal off has Method for measuring Degrees off Longitude upon Parallels off the Equator , ibid (1766)
An Inquiry into the Probable Parallax and Magnitude off the Fixed Stars , ibid (1767)
One the Twinkling off the Fixed Stars , ibid (1767)
One the Means off Discovering the Distance, Magnitude, &c., off the Fixed Stars , ibid (1784).

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