However, if the wave front reaches point B, then it will not only sweep all the ray paths with the same endpoints but also the infinitude of nearby paths. When two points A and B are specified, and a wave front is growing from point A, then it will sweep all the possible rays radiating from A.

Until the 19th century, nobody was aware that alternative paths traveling from one point to another are a fundamental property of waves. Initially, the principle was a controversial statement as it appeared to assign knowledge of nature’s intent. However, for the spherical surfaces, the time taken by the light ray is either maximum or minimum.įermat’s principle was stated by Pierre de Fermat in 1662 and is suitable to study optical devices. It means that a ray of light passing from one point to another chooses a certain path along which the time taken is minimum. For the refraction and reflection at the plane surfaces, Fermat’s Principle of Least Time holds. In 1662, Fermat demonstrated that a beam of light follows a path of the fastest time instead of a smaller distance. However, Fermat was able to determine the cause of the refractive behavior of light. Though the statement claimed was correct however, the observation has not addressed any cause. Dutch investigator Willebrord Snell in 1621 claimed that it is the sines of the angles of refraction and incidence that uphold a constant ratio. There was no simple relationship determined between the angles of refraction and incidence since 1621.

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