Refraction, Dip and Mirage
摘要
Light, or other wave energy, is assumed to travel in a straight line at uniform speed, provided the medium through which it is travelling has uniform properties. Thus, the speed of light in a vacuum is ‘c,’ but a light ray travelling through water will travel at an appreciably lower velocity, and in some peculiar forms of matter it is possible for light to travel at only a few meters per second.