Beginning of Essay
Imagine that we stand on any ordinary seaside pier, and watch the waves rolling in and striking against the colums of the pier. Large blue waves pay little attension to those columns - they divide right and left and unite after passing each column, much as a army ....

Middle of Essay
.... of the sea represent the sunlight. We know that the sunlight is a blend of lights of many colors - as we can prove for ourselves by passing it through a prism, or even through a jug of water, or as Nature demonstrates to us when she passes it through the raindrops of a summer shower and produces a rainbow. We also know that light consists of waves, and that the different colors of light are produced by waves of different lengths, red light by long waves and blue light by short waves. The mixture of waves which constitutes sunlight has to struggle through the obstacles it meets in the atmosphere, just as the mizture of waves at the seaside has to st ....