Opticks: or, A Treatise of the Reflexions, Refractions, Inflexions, and Colours of Light.

Newton defines colour through mathematics

First edition, first issue, without Newton's name on the title. Newton's Opticks expounds his corpuscular or emission theory of light, and first contains his important optical discoveries in collected form. It also prints two important mathematical treatises (omitted in later editions) describing his invention of the fluxional calculus, which are the grounds for his claim for priority over Leibniz.

Newton had arrived at most of his unconventional ideas on colour by about 1668; but when he first expressed them (tersely and partially) in public in 1672 and 1675, they had provoked hostile criticism, especially on the continent. The publication of Opticks, largely written by 1692, was held over by Newton until his most vociferous critics - especially Robert Hooke - were dead and, unusually for him, was first published in English, perhaps a further defensive measure. Nevertheless, Opticks established itself, from about 1715, as a model of the interweaving of theory with quantitative experimentation. The great achievement of the work was to show that colour was a mathematically definable property. Newton showed that white light was a mixture of infinitely varied coloured rays (manifest in the rainbow and the spectrum), each ray definable by the angle through which it is refracted on entering or leaving a given transparent medium. "Newton's Opticks did for light what his Principia had done for gravitation, namely place it on a scientific basis" (D. W. Brown, cited in Babson).