Interference and Diffraction
The colours of thin films are amongst the first phenomena which are well known to us and which can be attributed to the interference of light waves. If soap bubbles are produced by shaking a soap solution, these bubbles exhibit many beautiful colours. Then layers of turpentine and other substances spread upon the surface of water are also coloured. These phenomena are first mentioned by Boyle, whilst Hooke discovered that the colours vary with the thickness of the film. Newton investigated the phenomenon more closely, for which purpose he procured thin films of definite and known thickness. Diffraction phenomena, which are so fascinating when seen, have played a very important part in the history of optics. For the real reasons why Newton could not agree with the assumptions of the wave theory were not that he remained obstinate, in view of the fact that he had developed his own theory.