INTRODUCTION

In 1802 a youthful Thomas Young, British physician and scientist, had the audacity to resuscitate the wave theory of light (Young 1802). For this he was excoriated by Henry Brougham (1803) in the Edinburgh Review.

A discovery in mathematics, or a successful induction of facts, when once completed, cannot be too soon given to the world. But... an hypothesis is a work of fancy, useless in science, and fit only for the amusement of a vacant hour. (1803, p. 451)

This dramatic confrontation between Young and Brougham, it has been claimed, is but one example of a general methodological gulf between 19th-century wave theorists and 18th-and 19th-century particle theo­rists. The wave theorists, it has been urged by Larry Laudan (1981) and Geoffrey Cantor (1975), employed a method of hypothesis in defending their theory. This method was firmly rejected by particle theorists, who insisted, with Brougham, that the only way to proceed in physics is to make inductions from observations and experiments.

In Achinstein (1991), I argue, contra Laudan and Cantor, that 19th- century wave theorists, both in their practice and in their philosophical reflections on that practice, employed a method that is different from the method of hypothesis in important respects; moreover, there are strong sim­ilarities between the method the wave theorists practiced and preached and that of 19th-century particle theorists such as Brougham and David Brewster. In this chapter, I will focus just on the wave theorists. My aims are these: to review my claims about how in fact wave theorists typically argued for their theory; to see whether, or to what extent, this form of reasoning corresponds to the method of hypothesis or to inductivism in sophisticated versions of these doctrines offered by William Whewell and John Stuart Mill; and finally to deal with a problem of anomalies which I did not develop in Particles and Waves and might be said to pose a difficulty for my account.

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