If we look at the sky on a perfectly fine summer's day we shall find that the blue colour is the most pure and intense overhead，and when looking high up in a direction opposite to the sun。 Near the horizon it is always less bright，while in the region immediately around the sun it is more or less yellow. The reason of this is that near the horizon we look through a very great thickness of the lower atmosphere，which is full of the larger dust particles reflecting white ...>>more