Descartes generalized the theory for all colours, then translated it into mechanical imagery. Through a series of experiments performed in 1665 and 1666, in which the spectrum of a narrow beam was projected onto the wall of a darkened room, Isaac Newton denied the concept of modification and replaced it with that of analysis.

Basically, he denied the suggestion that light is simple and homogeneous. He concluded, instead that it is complex and heterogeneous and that the phenomena of colours manifest from the examination of the heterogeneous mixture into its simple components.

The ultimate source of Newton's belief that light is corpuscular was his recognition that individual beams of light have immutable criteria; in Newton's view, such properties imply immutable particles of matter. He held that individual rays that is, particles of given size excite sensations of individual colours as they impact against the retina of the eye. He also concluded that rays refract at distinct angles--hence, the prismatic spectrum, a beam of heterogeneous rays, i.e., alike incident on one face of a prism, separated or analyzed by the refraction into its component parts--and that phenomena such as the rainbow are produced by refractive analysis.

Because Neton believed that chromatic aberration could never be eliminated from lenses, Newton turned to reflecting telescopes; he constructed the first ever built. The heterogeneity of light has been the foundation of physical optics since his time.

There is no evidence that the theory of colours, fully described by Newton in his inaugural lectures at Cambridge, made any impression, just as there is no evidence that aspects of his mathematics and the content of the Principia, also pronounced from the podium, made any impression. Rather, the theory of colours, like his later work, was transmitted to the world through the Royal Society of London, which had been organized in 1660. When Newton was appointed Lucasian professor, his name was probably unknown in the Royal Society; in 1671, however, they heard of his reflecting telescope and asked to see it. Pleased by their enthusiastic reception of the telescope and by his election to the society, Newton volunteered a paper on light and colours early in 1672. On the whole, his dissitation was also well received, although a few questions and some dissent were muttered.

Primary among the dissenters to Newton's paper was Robert Hooke, a forceful figure within the Royal Society. Hooke considered himself the custodian of optics and hence he wrote a scathing critique of the young upstart. One can understand how the critique would have annoyed a normal man. The bitter rage it provoked, with the desire publicly to humiliate Hooke, however, bespoke the abnormal. Newton was unable rationally to confront criticism. Within a year of submitting the paper, he was so unsettled by the give and take of honest discussion that he began to cut his ties, and he withdrew into virtual isolation.

In 1675, during a visit to London, Newton thought he heard Hooke accept his theory of colours. He was emboldened to bring forth a second paper, an examination of the colour phenomena in thin films, which was identical to most of Book Two as it later appeared in the Optics.

The purpose of the paper was to explain the colours of solid bodies by showing how light can be analyzed into its components by reflection as well as refraction. His explanation of the colours of bodies has not survived, but the paper was significant in demonstrating for the first time the existence of periodic optical phenomena. He discovered the concentric coloured rings in the thin film of air between a lens and a flat sheet of glass; the distance between these concentric rings (Newton's rings) depends on the increasing thickness of the film of air. In 1704 Newton combined a revision of his optical lectures with the paper of 1675 and a small amount   Continued

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