The origins of length contraction: I. The FitzGerald-Lorentz deformation hypothesis

One of the widespread confusions concerning the history of the 1887 Michels on-Morley experiment has to do with the initial explanation of this celebra ted null result due independently to FitzGerald and Lorentz. In neither cas e was a strict, longitudinal length contraction hypothesis invoked, as is c ommonly supposed. Lorentz postulated, particularly in 1895, any one of a ce rtain family of possible deformation effects for rigid bodies in motion, in cluding purely transverse alteration, and expansion as well as contraction; FitzGerald may well have had the same family in mind. A careful analysis o f the Michelson-Morley experiment (which reveals a number of serious inadeq uacies in many textbook treatments) indeed shows that strict contraction is not required. (C) 2001 American Association of Physics Teachers.