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Physics in Perspective

, Volume 3, Issue 3, pp 258–270 | Cite as

Dispersion in the Ether: Light over the Water

  • Sir Brian Pippard

Abstract.

This is an account of measurements of the velocity of light by James Young (1811–1883) and George Forbes (1849–1936) around 1880 based upon an improved version of Fizeau's toothed-wheel method. They presented evidence for a dispersive effect resulting in a difference in the velocity of 1.8% across the visible spectrum. This conflicted with Albert A. Michelson's measurements and prompted discussions by Lord Rayleigh, Arthur Schuster, Léon Gouy, J. Willard Gibbs, and Paul Ehrenfest that led to the conclusion that not the phase velocity but the group velocity was being measured, and that there was no theoretical foundation for Young and Forbes's result.

Key words. Velocity of light, phase velocity, group velocity, James Young, George Forbes, Lord Rayleigh, Albert A. Michelson, Arthur Schuster, Léon Gouy, J. Willard Gibbs, Paul Ehrenfest. 

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Copyright information

© Birkhäuser Verlag Basel, 2001

Authors and Affiliations

  • Sir Brian Pippard
    • 1
  1. 1.Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE, UKGB

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