With all his work with light, Newton saw no such result. Try sketching the sum of the waves above. To give yourself a start, at each position of the dotted vertical lines, make an eye measure of the algebraic sum of the two original waves. When we say that waves diffract, we mean that they spread around barriers. You can hear the sound of a stereo around a corner from the speaker.
Some waves diffract better than others.
The deciding factor is the wavelength. In order for diffraction to occur, the barrier or opening must be comparable in size to the wavelength being considered. Newton decided that, since light casts shadows around objects and shows sharp images through small apetures, light does not diffract. It was not until almost 150 years later that Thomas Young devised an experiment to test Newtons hypothesis successfully. Go on to Part B .