Huygens' construction at Bowscale Tarn

 This is Bowscale Tarn, made famous by its mention in a poem by Wordsworth. He claimed that there were two immortal fish in it, and that attracted Victorian tourists. presumably if the fish are immortal, they are still there, but no sign of them today. However the pattern of waves on the water reminded me of Huygens' Construction.

Huygens suggested that you could predict where a wave would go next by marking a whole series of points along a wavefront and making these the sources of semi-circular ripples. Where the ripples overlap, that's where you get the next wavefront. Classes find that hard to believe, but it does work. Today the waves were being driven from left to right by the wind. From above they looked like good plane wavefronts until you magnify the picture. Then the wavefronts seem to be broken up into smaller sections, reminiscent of sets of semi-circular ripples. For diagrams and a further explanation see http://ipodphysics.com/huygen-principle.php