Newton showed that every colour has a unique angle of refraction that can be calculated using a suitable prism. Newton chose the number seven because of the ancient Greek belief that seven is a mystical number. Newton introduced the term ‘colour spectrum’ and although the spectrum appears continuous, with no distinct boundaries between the colours, he chose to divide it into seven: red, orange, yellow, green, blue, indigo, and violet. Newton concluded that light is composed of coloured particles that combine to appear white. Since almost everyone agreed that light must be composed of either particles or waves, Newton used the failure of the wave theory to prove that light is made of particles. Newton claimed this was a ‘crucial experiment’.Ī crucial experiment is an experiment that is devised to decide between two contradictory theories, where the failure of one determines the certainty of the other.

This showed that the colour spectrum is not caused by glass corrupting the light. To prove that this was false, Newton passed a beam of white light through two prisms, which were held at such an angle that it split into a spectrum when passing through the first prism and was recomposed, back into white light, by the second prism (as shown in Figure 3.1). This means that the more glass the light travels through, the more corrupt it will become. Īdvocates of the wave theory had previously stated that light waves are made of white light and that the colour spectrum that can be seen through a prism is formed because of corruption within the glass.

He argued that the geometric nature of the laws of reflection and refraction could only be explained if light is made of particles, which he referred to as corpuscles, as waves don’t tend to travel in straight lines.Īfter joining the Royal Society of London in 1672, Newton stated that the 44th trail in a series of experiments he had previously conducted proved that light is made of particles and not waves. Newton claimed that Grimaldi’s diffraction was simply a new kind of refraction. The English natural philosopher Isaac Newton bought his first prism in 1666, one year after Francesco Grimaldi’s work on diffraction was published. Reflection, Refraction, and DiffractionĢ0.

Newton opticks