Isaac Newton first discussed the coloured interference fringes that we now call Newton's Rings in a communication to the Royal Society in December 1675. His book Opticks' further expanded on his ideas. The original observation was made with a wedge-shaped air-gap between the surfaces of two prisms, although the standard technique now is to press a convex surface of a lens against a flat glass plate.
Newton discovered concentric coloured rings in the thin film of air between a lens and a flat sheet of glass. The distance between these concentric rings depended on the increasing thickness of the film of the air.[a] .
At the time numerous pieces of equipment were made to generate the interference patterns. The best device was made by a French optician, Duboscq. .
Newton's rings demonstrate the wave-like nature of light (though Newton himself did not believe in the wave-like behaviour of light).
[b].
Because Newton opposed the wave theory of light, Huyghens superposition theory was not accepted until one hundred and fifty years later. The turning point in accepting the wave theory of light came in 1818 when Fresnel wrote a brilliant memoir on diffraction. [c].
Theory.
Interference results from the superposition of two waves at the same point in space. The waves are said to interfere constructively if they are in phase or destructively if they are out of phase. Constructive interference creates bright fringes and destructive interference creates dark fringes.
Interferometry can be used to measure tiny distances (practically, the radius of curvature of a lens can be determined). Refractive indices of materials can also be found. .
The rings are best observed with a monochromatic light source. A monochromatic source shows the bright and dark fringes clearly (without the colourful pattern).
As a beam passes through the lens, light on the lower surface of the lens is partially reflected (shown a beam A in diagram 1) but also partially transmitted.