‘A Letter of Mr. Isaac Newton ... containing his New Theory about Light and Colors: Where Light is declared to be not Similar or Homogeneal, but consisting of difform rays, some of which are more refrangible than others: And Colors are affirm'd to be not Qualifications of Light, deriv'd from Refractions of natural Bodies, ...

London: John Martyn, [1671/1672].

First printing of Newton’s seminal discoveries on the nature of light. This is Newton’s first published paper, and arguably the most important paper in the history of optics. “If he had published nothing else, it would be sufficient of itself to guarantee him a place among the immortals of modern science” (Christianson, p. 152). “When he was first appointed to the chair of Lucasian Professor at Cambridge, Newton chose optics for the subject of his lectures and researches, and before the end of 1669 he had worked out the details of his discovery of the decomposition of a ray of white light into rays of different colours by means of a prism. The complete explanation of the theory of the rainbow followed from this discovery. These discoveries formed the subject-matter of the lectures which he delivered as Lucasian professor in the years 1669, 1670 and 1671. The chief new results were embodied in a paper communicated to the Royal Society in February 1672, and subsequently published in the Philosophical Transactions [as offered here]. Before Newton, light was believed to be a homogeneous entity and color a mixture of light with darkness; the prism was itself believed to provide the darkness coloring light, and it was thought that all rays of white light striking a prism at the same angle would be equally refracted. Through his experiment, however, Newton came to the revolutionary conclusion that white light was n fact a mixture of many different types of rays, and that the prism split white light into a ‘rainbow spectrum’ of rays – each of which was refracted at a slightly different angle through the prism, and each of which was responsible for producing a given spectral color. In his experiments, Newton set up a prism near his window and projected a spectrum on the far wall (22 feet away). To prove that the prism in fact refracted and didn’t itself color the white light, Newton refracted the light back again. A ‘crucial experiment’ confirmed the theory: Newton selected out of spectrum a narrow band of light of one color and sent it thru a second prism; no further elongation or refraction of the ray occurred – thus confirming the theory” (ibid.). The reception of Newton’s paper was mixed, to say the least. Many simply ignored it. Others denied the experimental facts. “Mariotte in 1679, Pardies in 1672 and Linus in 1675 all claimed that they had failed to replicate the basic experiments described by Newton. Unwilling to enter into detailed argument, Newton responded by asking his critics to repeat carefully his experiments. They did and without success.” Others, such as Hooke, who confirmed Newton’s experimental results by performing the experiments himself before a committee of the Royal Society in April 1676, believed that they could be accounted for by minor modifications of existing theories, making Newton’s radical ideas unnecessary. The controversy continued for some six years after the appearance of the paper, and made Newton wary of publication in the future.

Newton’s studies of light and optics began very early, possibly even before 1665, but were interrupted by the plague, and only resumed two years later. Appointed in 1669 to the Lucasian Chair of Mathematics at Cambridge, he was obliged by the statutes of the post to lecture and to deposit his lectures in the University Library. For the period 1670-1672 Newton lectured on optics and deposited the lectures in October 1674. Although he considered publishing the lectures together with an early tract on calculus, De methodus fluxionum, neither was published until after his death.

Newton’s optical work first came to the attention of the Royal Society when Newton exhibited there a telescope he had made. He was elected a fellow shortly thereafter, on 11 January 1672, and responded by offering the Society an account of the discoveries that had led him to his invention. This was his ‘New theory about light and colours,’ published in the Philosophical Transactions on 19 February 1672.

“The paper or letter begins straightforwardly enough. In the first few pages Newton describes his surprise at the elongation of the spectrum formed by shining a beam of light through a glass prism in a darkened room, in the direction normal to the axis of the prism; and relates how he was drawn on to the ‘crucial experiment’ wherein he refracted the separated coloured rays through a second prism parallel to the first and then measured, one by one, their unlike refractions.

‘And so the true cause of the length of that image [spectrum] was detected to be no other, than that Light consists of Rays differently refrangible, which, without any respect to a difference of their incidence, were, according to their degrees of refrangibility, transmitted towards divers points of the wall.’

“Newton’s terse and polished narrative was a highly artificial reconstruction of what actually happened, and therefore some writers have been inclined to infer that Newton’s most famous experiment may have been as imaginary as it was crucial, at least in its precise details. But even if the experiment was a heuristic device, it was a concise representation of much solid experience. Among his contemporaries, Newton’s real difficulties began with the next paragraph of the paper in which, without further justification of his inference, Newton boldly declared that ‘Light itself is a Heterogeneous mixture of differently refrangible Rays.’

“This, his second philosophical discovery, and surely in his own mind that of deeper significance, in a rather curious way Newton failed to examine in detail in the paper. Instead he argued (correctly) for the greater significance of chromatic aberration as compared with spherical aberration as an imperfection in lenses, and the laid down a ‘doctrine’ of colours:

‘not as Hypothesis but most rigid consequence, not conjectured by barely inferring ‘tis thus because not otherwise or because it satisfies all phenomena (the Philosopjer’s universall topic) but evinced by the mediation of experiments concluding directly & without any suspicion of doubt.’

“Briefly, the ‘doctrine’ embraces the following propositions:

  1. A specific refrangibility is in one-to-one correspondence with each colour; so the science of colours is mathematica (in relation to refraction);
  2. This correspondence is fixed and unalterable;
  3. Primary colours are constant, homogeneous and unchangeable; compounded colours may be formed from them, and again resolved into their elements by refraction;
  4. Refraction analyses heterogeneous white light into its homogeneous coloured constituents, separated as distinct rays;
  5. Reflection also analyses white light, reflecting surfaces returning one or more constituents more copiously and then appearing of the appropriate colour.

“It will be noted that Newton here suppressed his belief that the variety of refrangible rays is infinite (though the shading of colour perceived by the eye is not); the borders of the orange band in the spectrum, for example, must have diverged through refraction, or the band would appear infinitely narrow.

“Newton concluded with notes on the precautions to be observed in repeating his experiments, if they were to reveal the same phenomena that he had detected. He added the experiment in which refracted light was reunited by a large lens, describing the effect of blocking a colour so that its light does not reach the lens” (Hall, pp. 61-62).

The implications of his work for the design of optical instruments – the problem of chromatic aberration – did not escape Newton. “As a practical consequence of his theoretical insights Newton pointed out a limit to the perfection obtainable by telescopes. Any glass, he argued, so ‘exactly figured as to collect any one sort of rays into one point’, would not thereby be capable of collecting at the same point all other rays. It led him ‘by degrees’ to the development of a novel kind of instrument, the reflecting telescope, with which he could discern Jupiter’s satellites and Venus’s phases” (Gjertsen, p. 375).

Although Newton presented his theories as being the result of a Baconian induction from experiment, examination of his contemporary notebooks shows that very early in his optical research Newton was explaining his experiments by ‘the corpuscular hypothesis,’ according to which light rays are composed of “very small bodies emitted from shining substances”. In his Philosophical Notebook, probably begun in early 1664, Newton wrote: “Blue rays are reflected more than red rays, because they are slower. Each colour is caused by uniformly moving globuli. The uniform motion which gives the sensation of one colour is different from the motion which gives the sensation of any other colour.” It seems that Newton’s great leap forward was actually a consequence of implications drawn from profound scientific speculation and insight

“Newton’s ‘New Theory of Colours’ astounded his contemporaries; some of the best qualified judges among them, including Robert Hooke, were unable to accept or even comprehend it. A major feature baffling them was Newton’s insistence that whiteness is a mixture of all colours. If white sunlight is not pure and elemental, as all men believed, why could it not equally ell be the result of combining two elemental colours only (on the universal principle of dichotomy)? Newton deals with this matter in a number of letters written in the months following the publication of his first paper, confessing that ‘this assertion (the production of whiteness by mixtures) above the rest appears Paradoxicall, & is with most difficulty admitted’” (Hall, p. 44). Mariotte in 1679, Pardies in 1672 and Linus in 1675 all claimed that they had failed to replicate the basic experiments described by Newton. Unwilling to enter into detailed argument, Newton responded by asking his critics to repeat carefully his experiments. They did and without success. The controversy continued for some six years after the appearance of the paper, and made Newton wary of publication in the future.

Newton decided to answer his critics by preparing a more comprehensive account of his experiments and discoveries, and this was begun soon after the publication of the present paper. A first draft was sent to the Royal Society in 1675, but remained unpublished. Newton returned to the project in 1687, after publication of Principia, but nothing was published until 1704.

The original manuscript of Newton’s ‘New theory’ is lost, but a copy in the hand of John Wickins, Newton’s ‘chamber fellow’ as a Cambridge student and his closest friend for some twenty years, is preserved in Cambridge University Library.

Babson 165. Dibner, Heralds of Science, 144. Evans 5. Gray 231, no. 1. Grolier/Horblit 79a. Lilly/Westfall 79. Sparrow 54. Wallis 231 (1). Christianson, In the Presence of the Creator, 1984; Gjertsen, Newton Handbook, 1986; Westfall, Never at rest, 1980.



[Complete volume] 4to (221 x 168 mm), pp. [iv], 2087-2299, 3000-3095, with 5 engraved plates. Contemporary panelled calf.

Item #5191

Price: $45,000.00

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