#physics

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Swiss mathematician Johann Jakob Balmer was born in 1825.

Balmer is most renowned for his discovery of the Balmer series, a formula used to predict the wavelengths of visible light emitted by hydrogen. In 1885, he was interested in the spectral lines of hydrogen observed in the sun's spectrum. He then proposed an empirical formula to predict the wavelengths of the visible lines of the hydrogen spectrum.

https://en.wikipedia.org/wiki/Balmer_series

Johann Jakob Balmer - Reproduction of a public domain painting. Black and white photograph of an older gentleman with spectacles.

The usual approach to detecting dark matter is to search for particles with a specific range of masses. The hope is that even if we see nothing, we'll at least know more about what dark matter is *not*.

Physicists at Fermilab have now released the first data from a different type of detector, one that looks for dark matter over a much wider range at lower sensitivity.

Result: still no dark matter, but a larger swathe of parameter space ruled out.

https://physicsworld.com/a/bread-experiment-tracks-dark-photons-to-new-levels/

in 1905. Albert Einstein completes his doctoral thesis at the University of Zurich.

Titled "Eine neue Bestimmung der Moleküldimensionen", he calculated the size of sugar molecules in solution and from this a value for the Avogadro constant. It is related to his work on Brownian motion, published in the same year, and supported the atomic hypothesis, which was still controversial among leading physicists at the time.

Books by Albert Einstein at PG:
https://www.gutenberg.org/ebooks/author/1630

Cover image of the Ph.D. dissertation of Albert Einstein defended in 1905 at ETH Zürich. Einstein's 1905 dissertation, Eine neue Be­stimm­ung der Mol­e­kül­di­men­si­one ("A new deter­mi­na­tion of mo­lec­u­lar di­men­sions")

in 1897.

J. J. Thomson of the Cavendish Laboratory announces his discovery of the electron as a subatomic particle, over 1,800 times smaller than a proton (in the atomic nucleus), at a lecture at the Royal Institution in London.

Thomson showed that cathode rays were composed of previously unknown negatively charged particles (now called electrons), which he calculated must have bodies much smaller than atoms and a very large charge-to-mass ratio.

https://www.gutenberg.org/ebooks/author/38322

English physicist J J Thomson. Black and white photo featuring J J Thomson sporting glasses and a mustache.
The cathode ray tube by which J. J. Thomson demonstrated that cathode rays could be deflected by a magnetic field, and that their negative charge was not a separate phenomenon JJ Thomson - Philosophical Magazine, 44, 293 (1897)

French mathematician and physicist Henri Poincaré was born in 1854.

He is considered one of the founders of the field of topology. He was among the first to present the Lorentz transformations, part of the groundwork for Albert Einstein’s theory of special relativity. Poincaré also studied the behavior of planetary orbits and contributed to the three-body problem in celestial mechanics, exploring the stability and motion of celestial bodies.

Couverture du livre "La science et l’hypothèse" de Henri Poincaré Henri Poincaré, Ernest Flammarion éditeur .
Henri Poincaré Unknown author - Popular Science Monthly Volume 82 A black and white photo of a bearded man wearing glasses.

American mathematical physicist J. Willard Gibbs died in 1903.

Gibbs' most celebrated contributions were in the field of thermodynamics, particularly concerning the phase rule, chemical potential, and Gibbs free energy—a concept named after him. The Gibbs free energy is particularly critical in predicting the direction of chemical reactions and phase changes. His book, "Elementary Principles in Statistical Mechanics," laid the foundation for modern statistical mechanics.

Maxwell's sketch of the lines of constant temperature and pressure, made in preparation for his construction of a solid model based on Gibbs's definition of a thermodynamic surface for water (see Maxwell's thermodynamic surface) James Clerk Maxwell (1831 – 1879) - P. M. Harman (ed.), The Scientific Letters and Papers of James Clerk Maxwell, vol. 3, 1874-1879, (Cambridge, UK: Cambridge University Press, 2002), p. 232, plate IV. J. C. Maxwell's sketch of the thermodynamic surface for a water-like substance, based on a theoretical construct proposed by J. W. Gibbs. The curves are "isothermals and isopiestics drawn by help of the Sun."
Portrait of American mathematical physicist J. Willard Gibbs, taken about 1895 Photograph taken around 1895. According to his student Lynde Wheeler, of the existing portraits, this is the most faithful to Gibbs's kindly habitual expression. Unknown author - Scanned from the frontispiece for Raymond J. Seeger, Men of Physics: J. Willard Gibbs, American Mathematical Physicist par excellence, (Oxford and New York: Pergamon Press, 1974). Used also as the frontispiece for Lynde P. Wheeler, Josiah Willard Gibbs, The History of a Great Mind, (New Haven: Yale University Press, 1951). No copyright notice or attribution is given in either book.

German physicist Arnold Sommerfeld died in 1951.

In 1916, he introduced the idea of elliptical orbits for electrons, and he also introduced additional quantum numbers which included the azimuthal quantum number and magnetic quantum number. He also introduced a dimensionless physical constant known as the fine-structure constant. This constant characterizes the strength of the electromagnetic interaction between elementary charged particles.

https://www.gutenberg.org/ebooks/16264

Title page of the book "Atomic Structure and Spectral Lines" by Arnold Sommerfeld, translated by Henry L. Brose, with 125 figures, published by Methuen & Co. Ltd., London.
Sommerfeld c. 1922–1923 Bain News Service, publisher - Library of Congress Catalog: https://lccn.loc.gov/2014715010. A vintage black and white portrait of a person in a dark jacket and collared shirt with the top of the image labeled "A. SOMMERFELD" and "38777" on the right side. The edges of the photograph are irregular and worn, adding to the aged appearance.

French mathematician and physicist Siméon-Denis Poisson died in 1840.

He is known for his significant contributions to mathematical physics, particularly in the fields of mechanics, probability theory, and electricity. He made crucial advancements in understanding the behavior of fluids & the mathematical treatment of physical phenomena. Some of his most notable contributions include: Poisson distribution, potential theory, fluid mechanics, electromagnetism.

Siméon Denis Poisson François-Séraphin Delpech / After Nicolas Eustache Maurin Black and white portrait of Siméon Denis Poisson wearing a formal 19th-century coat with a cravat tied around the collar of his shirt. The figure is depicted from the chest up and the artwork includes signatures at the bottom with the word "POISSON" prominently featured in the center.
Mémoire sur le calcul numerique des integrales définies. Par M. Poisson... - [S.l.] : [s.n.], [1826]. - 34 p. ; 4º. Image shows the first page of an old mathematical paper titled "MÉMOIRE Sur le calcul numérique des Intégrales définies" by M. Poisson, dated 11th December 1826, addressed to the Academy of Sciences. The text is in French and discusses numerical calculation of definite integrals and its various applications in geometry and physics.

Swedish astronomer, physicist, and mathematician Anders Celsius died in 1744.

In 1742, Celsius introduced the temperature scale that bears his name. His original scale was actually the reverse of what we use today: it set the boiling point of water at 0 degrees & the freezing point at 100 degrees. However, shortly after his death, the scale was reversed by Carl Linnaeus, resulting in the 0 degrees for freezing & 100 degrees for boiling that we are familiar with.

Headshot of Anders Celsius Portrait of Anders Celsius in historical dress with a powdered wig, wearing a dark coat with a white ruffled collar.
De novo in fluviis norlandiarum piscandi modo, 1738 Anders Celsius - Available in the BEIC digital library and uploaded in partnership with BEIC Foundation.
Headshot of Anders Celsius Portrait of Anders Celsius in historical dress with a powdered wig, wearing a dark coat with a white ruffled collar.
"Observationer om twänne beständiga grader på en thermometer" [Observations about two stable degrees on a thermometer]. Kungliga Svenska Vetenskapsakademiens Handlingar (Proceedings of the Royal Swedish Academy of Sciences) (in Swedish). 3: 171–180. 1742.