Hermann von Helmholtz
Hermann von Helmholtz | |
|---|---|
| Born | 31 August 1821 Potsdam, Prussia |
| Died | 8 September 1894 (aged 73) Charlottenburg, Berlin, German Empire |
| Nationality | German |
| Known for | Conservation of energy, vortex theorems, physiological optics and acoustics |
| Scientific career | |
| Fields | Physics, Physiology, Mathematics |
| Institutions | University of Königsberg; University of Bonn; University of Heidelberg; University of Berlin |
Hermann Ludwig Ferdinand von Helmholtz (31 August 1821 – 8 September 1894) was a German physician, physiologist and physicist, and one of the last people able to work at the front of several sciences at once. He gave the conservation of energy its first general statement, proved the theorems that govern vortex motion in an ideal fluid, and founded the modern study of vision and hearing.
Trained as an army surgeon because his family could not afford a physics education, Helmholtz published Über die Erhaltung der Kraft ("On the Conservation of Force") in 1847 at the age of twenty-six, arguing that mechanical, thermal, electrical and chemical processes all exchange a single conserved quantity. In physiology he measured the speed of nerve conduction — found to be finite and surprisingly slow, of the order of tens of metres per second — invented the ophthalmoscope in 1851, developed the Young–Helmholtz trichromatic theory of colour vision, and in Die Lehre von den Tonempfindungen (1863) explained musical timbre in terms of harmonic content, introducing the Helmholtz resonator. The Helmholtz free energy is named for him, as is the Kelvin–Helmholtz contraction timescale for stellar energy release by gravitational collapse. He taught Heinrich Hertz, Max Planck, Wilhelm Wien and Michelson.
Vortex theorems and the vortex atom
In 1858 Helmholtz published "Über Integrale der hydrodynamischen Gleichungen, welche den Wirbelbewegungen entsprechen," establishing the behaviour of vorticity in an inviscid, incompressible fluid: vortex lines move with the fluid, the strength of a vortex tube is constant along its length and constant in time, and a vortex tube cannot begin or end within the fluid — it must close on itself or reach a boundary. A vortex ring, once formed, is therefore permanent.
That permanence is why the theorems matter far beyond hydrodynamics. Reading Helmholtz and watching Tait's smoke-ring demonstrations, William Thomson (Lord Kelvin) proposed in 1867 that atoms are vortex rings in the aether: indestructible by Helmholtz's theorem, distinguishable by their knotting and linking, and capable of vibration to give spectral lines. The vortex atom occupied British physics for some thirty years before being abandoned with the aether itself.
On this wiki
Helmholtz appears here chiefly as the ancestor of the vortex and toroidal-ring models of matter catalogued in Category:Vortex Theory and at Toroidal Ring. His theorems supply the reason such models are attempted at all: they are the classical demonstration that a fluid can hold stable, self-perpetuating, individually identifiable structures, which is precisely what a particle theory built on a medium requires.
- Paramahamsa Tewari's "On the Space-Vortex Structure of the Electron" (2005) builds the electron itself as a vortex structure in space.
- Carl Frederick Krafft's The Ether and its Vortices (1955) and Ether and Matter (1945) are the wiki's most sustained development of the vortex-atom line.
- "An Interpretation of Faraday's Lines of Force" treats a magnetic line of force as a closed toroidal ring vortex, joining Helmholtz's theorems directly to Faraday's picture of the field; Edward M Kelly's "The Mechanics of Faraday's Law in the Vortex Sponge" works induction out in a vortex medium.
- Giuseppe Cannata's "Electromagnetism in Ether" (1999) and much of Category:Aether rest on the same hydrodynamic analogy.
Helmholtz against Weber. In the early 1870s Helmholtz mounted the most damaging theoretical attack on Weber's velocity-dependent force law, arguing that it implied a charge could behave as though it had negative effective mass at sufficiently small separations, so that energy could be extracted without limit — a violation of the conservation principle Helmholtz himself had established. Weber replied that the objection applied only to configurations outside the law's physical range. The exchange did more than anything else to end Weber electrodynamics as a live research programme in Germany.
That verdict is disputed on this wiki. Andre K T Assis has reconstructed the Weber–Helmholtz debate in Weber's favour, and Thomas E Phipps revisits the force law in "Toward Modernization of Weber's Force Law" (Physics Essays, 1990) and "Weber-type Laws of Action-at-a-Distance in Modern Physics" (Apeiron, 1990). Peter Graneau's "Red and Green Potential Energy" (1997) takes up the energy-accounting question that Helmholtz's objection turns on. See Category:Electrodynamics.