THE PAPER ON COLORS that Newton sent to the Royal Society early in 1672 in the form of a letter addressed to Henry Oldenburg did not contain anything new from Newton's point of view. The occasion provided by the telescope had come at an opportune time. At Barrow's behest, Newton had been revising Barrow's lectures for publication during the winter. He had not found it a great chore to produce a succinct statement of his own theory buttressed by three prismatic experiments that he took to be most compelling. He thought it relevant to include a special discussion of how the discovery had led him to devise the reflecting telescope. The continuing correspondence provoked by the initial paper, which intruded intermittently on his time and consciousness during the following six years, also involved only one addition to his optics, his introduction to diffraction and brief investigation of it. Aside from diffraction, the entire thrust of his concern with optics during the period was the exposition of a theory already elaborated.

The continuing discussion forced Newton to clarify some issues. When he wrote in 1672, he had not yet fully separated the issue of heterogeneity from his corpuscular conception of light, and he allowed himself to assert that, because of his discovery, it could “be no longer disputed . . . whether Light be a Body.” He could hardly have been more mistaken. Within a week of the paper's presentation, Robert Hooke produced a critique that mistook corpuscularity for its central argument and proceeded to dispute it with some asperity. The lesson was not wasted. Though he continued to believe in the corpuscular conception, Newton learned to insist that the essence of his theory of colors lay in heterogeneity alone. This was a matter of clarification and exposition, however, not an alteration of his theory. The very fact that six years of discussion effected no change, such that his Opticks, finally published in 1704, merely restated conclusions worked out in the late 1660s, testifies to the intensity and rigor of the early investigation.

The discussion that followed on the paper of 1672 tells us less about optics than about Newton. For eight years he had locked himself in a remorseless struggle with Truth. Genius of Newton's order exacts a toll.