THE RECEIVED VIEW
See Meyering (1989) for a detailed study of how thoroughly philosophical and empirical developments interact in the history of optics and perception theory.
These laws were based on the law of sines discovered by Snell. As several scholars have noted, Newton's presentation here is misleading. The laws of optics at the time did in fact predict an oblong or elongated image, except for one position of the prism with respect to the beam of light, that of minimum deviation. Newton indicates that this was indeed the position of the prism only later in the letter. Furthermore, although the received laws did predict a circular image for the position of minimum deviation, this implication was not immediately obvious, but required a long geometrical demonstration. Newton's surprise would be shared, then, only by readers who were mathematically sophisticated or familiar with the demonstration. See Sabra (1967/1981: Chapter 9, especially 235-7). See also the extensive discussion of Newton's letter in Sepper (1988: Chapter 3, especially 107-9).
My summary and criticism of Newton's argument are based on Sabra (1967/1981:249-50, 295).
One of the reasons for Newton's insistence was that he had specific views on the nature of hypotheses in science. A hypothesis was a proposition that was not rigorously deduced from experiments, but was merely supposed in order to explain experiments. A hypothesis had therefore only an approximate degree of truth, and so was strictly speaking false. Differential refrangibility according to colour was not a hypothesis for Newton because he claimed that it followed rigorously from his crucial experiment. See Sabra (1967/1981:274-6).
Sabra (1967/1981:250) warned against this way of speaking, but his warning seems to have gone unheard. Thus Henry Guerlac writes: 'Having established this fact [of differential refrangibility], Newton then set forth in thirteen numbered paragraphs his "doctrine"
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Book title: Colour Vision: A Study in Cognitive Science and the Philosophy of Perception.
Contributors: Evan Thompson - Author.
Place of publication: New York.
Publication year: 1995.
Page number: 304.
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