Preparing for Lower Sixth Physics #4: Huygens' construction in Portpatrick harbour

Looking down over the side of Portpatrick harbour, I noticed that the plane waves hitting the sides of the harbour were getting reflected back as semi-circular ripples. There must have been bits sticking out a little bit further than usual, but it reminded me of Huygens' construction. Christiaan Huygens was a Dutch physicist who was a contemporary of Isaac Newton. He suggested that light was a wave: Newton held that light was made of small particles called corpuscles. You can explain reflection and refraction with either waves or particles. It took Thomas Young's double slit experiment 200 years later to tip the balance in favour of the wave theory. Another different between Newton and Huygens was that Newton favoured using rays - arrows to show the direction in which the wave is moving. You can't see these in my photograph. You can see the crests of the waves. These are called wavefronts. Huygens' construction uses a technique called "secondary wavelets" to predict where the next wavefront will appear. He split the wave into individual points which then made their own semi-circular ripples like the ones I saw in the harbour, Then he drew the next wavefront along the front of the secondary wavelets. See below: