# Famous Physicists 1800-1950

Christian Doppler | 1803-1853 Austrian |
experimented with sound waves; derived an expression for the apparent change in wavelength of a wave due to relative motion between the source and observer |

Wilhelm E. Weber | 1804-1891 German |
developed sensitive magnetometers; worked in electrodynamics and the electrical structure of matter |

Sir William Hamilton | 1805-1865 Irish |
developed the principle of least action and the Hamiltonian form of classical mechanics |

James Prescott Joule | 1818-1889 British |
discovered mechanical equivalent of heat |

Armand-Hippolyte-Louis Fizeau | 1819-1896 French |
made the first terrestrial measurement of the speed of light; invented one of the first interferometers; took the first pictures of the Sun on daguerreotypes; argued that the Doppler effect with respect to sound should also apply to any wave motion, particularly that of light |

Jean-Bernard-Léon Foucault | 1819-1868 French |
accurately measured speed of light; invented the gyroscope; demonstrated the Earth’s rotation |

Sir George Gabriel Stokes | 1819-1903 British |
described the motion of viscous fluids by independently discovering the Navier-Stokes equations of fluid mechanics (or hydrodynamics); developed Stokes theorem by which certain surface integrals may be reduced to line integrals; discovered fluorescence |

Hermann von Helmholtz | 1821-1894 German |
developed first law of thermodynamics, a statement of conservation of energy |

Rudolf Clausius | 1822-1888 German |
developed second law of thermodynamics, a statement that the entropy of the Universe always increases |

Lord Kelvin (born William Thomson) |
1824-1907 British |
proposed absolute temperature scale, of essence to development of thermodynamics |

Gustav Kirchhoff | 1824-1887 German |
developed three laws of spectral analysis and three rules of electric circuit analysis; also contributed to optics |

Johann Balmer | 1825-1898 Swiss |
developed empirical formula to describe hydrogen spectrum |

Sir Joseph Wilson Swan | 1828-1914 British |
developed a carbon-filament incandescent light; patented the carbon process for printing photographs in permanent pigment |

James Clerk Maxwell | 1831-1879 Scottish |
propounded the theory of electromagnetism; developed the kinetic theory of gases |

Josef Stefan | 1835-1893 Austrian |
studied blackbody radiation |

Ernst Mach | 1838-1916 Austrian |
studied conditions that occur when an object moves through a fluid at high speed (the “Mach number” gives the ratio of the speed of the object to the speed of sound in the fluid); proposed “Mach’s principle,” which states that the inertia of an object is due to the interaction between the object and the rest of the universe |

Josiah Gibbs | 1839-1903 American |
developed chemical thermodynamics; introduced concepts of free energy and chemical potential |

James Dewar | 1842-1923 British |
liquified nitrogen and invented the Dewar flask, which is critical for low-temperature work |

Osborne Reynolds | 1842-1912 British |
contributed to the fields of hydraulics and hydrodynamics; developed mathematical framework for turbulence and introduced the “Reynolds number,” which provides a criterion for dynamic similarity and correct modeling in many fluid-flow experiments |

Ludwig Boltzmann | 1844-1906 Austrian |
developed statistical mechanics and applied it to kinetic theory of gases |

Roland Eötvös | 1848-1919 Hungarian |
demonstrated equivalence of gravitational and inertial mass |

Oliver Heaviside | 1850-1925 English |
contributed to the development of electromagnetism; introduced operational calculus and invented the modern notation for vector calculus; predicted existence of the Heaviside layer (a layer of the Earth’s ionosphere) |

George Francis FitzGerald | 1851-1901 Irish |
hypothesized foreshortening of moving bodies (Lorentz-FitzGerald contraction) to explain the result of the Michelson-Morley experiment |

John Henry Poynting | 1852-1914 British |
demonstrated that the energy flow of electromagnetic waves could be calculated by an equation (now called Poynting’s vector) |

Henri Poincaré | 1854-1912 French |
founded qualitative dynamics (the mathematical theory of dynamical systems); created topology; contributed to solution of the three-body problem; first described many properties of deterministic chaos; contributed to the development of special relativity |

Janne Rydberg | 1854-1919 Swedish |
analyzed the spectra of many elements; discovered many line series were described by a formula that depended on a universal constant (the Rydberg constant) |

Edwin H. Hall | 1855-1938 American |
discovered the “Hall effect,” which occurs when charge carriers moving through a material are deflected because of an applied magnetic field – the deflection results in a potential difference across the side of the material that is transverse to both the magnetic field and the current direction |

Heinrich Hertz | 1857-1894 German |
worked on electromagnetic phenomena; discovered radio waves and the photoelectric effect |

Nikola Tesla | 1857-1943 Serbian-born American |
created alternating current |