THEODORE ARABATZZS” THE DISCOVERY OF THE ZEEMAN EFFECT: A CASE STUDY OF THE INTERPLAY BETWEEN THEORY AND EXPERIMENT 1. Introduction THE ANALYSIS of experimentation is a relatively new trend in history and philosophy of science. After the demise of logical positivism both disciplines tended to focus on the theoretical aspects of science and played down the autonomy and importance of experimental life. The theoretical orientation of post-positivistic studies of science and their concomitant ‘neglect of experi- ment’ has been criticized on both historical and philosophical grounds. A group of historians and philosophers of science has recently protested against the neglect of experiment and instrumentation, and attempted a historical and philosophical exploration of experimental science. The outcome of this criti- cism is a developing experiment-orientated history and philosophy of science.’ Three aspects of the historical and philosophical commentary on experimen- tation deserve special mention. First, the focus of analysis has moved away *Program in History of Science, Department of History, Princeton University, Princeton, NJ 08544, U.S.A. Received 3 April 1991; in revised form 30 December 199 I. ‘The pioneering step in this direction was made by Ian Hacking, Representing and Intervening (Cambridge: Cambridge University Press. 1983). Other significant contributions to the same subject include Peter Achinstein and Owen Hannaway (eds), Observation, Experiment. and Hypothesis in Modern Physical Science (Cambridge, Massachusetts: MIT Press, 1985); Allan Franklin, The Neglecf oj Experiment (Cambridge: Cambridge University Press, 1986); Peter L. Galison, How E.xperiments End (Chicago: University of Chicago Press, 1987); David Gooding. Trevor Pinch, and Simon Schaffer (eds), The Uses of Experiment: Studies in the Natural Sciences (Cambridge: Cambridge University Press, 1989); the collection of essays in Timothy Lenoir and Yehuda Elkana (eds), ‘Practice, Context, and the Dialogue between Theory and Experiment’, Science in Context 2 (1988) No. 1; and Steven Shapin and Simon Schaffer, Leviathan and the Air-Pump: Hobbes. Boyle, and the E.wperimentol Life (Princeton, New Jersey: Princeton University Press, 1985). For a recent overview of the philosophy of experiment see Ian Hacking, ‘Philosophers of Experiment’, in Arthur Fine and Jarrett Leplin (eds), PSA 1988: Proceedings qj’ the 1988 Biennial Meeting of the Philosophy oJ Science A$ociation, Vol. 2 ‘Symposia and Invited Papers’ (East Lansing, Michigan: Philosophy of Science Association, 1989), pp. 147-156. Another useful and up to date survey of studies of experimentation, which focuses on works written from a sociological perspective, is Jan Golinski, ‘The Theory of Practice and the Practice of Theory: Sociological Approaches in the History of Science’. Isis 81 (1990), 492-505. Stud. Hist. Phil. Sci., Vol. 23, No. 3, pp. 3655388. 1992. 0039-3681/92 S5.00f0.00 Printed in Great Britain 0 1992. Pergamon Press Ltd 365