@Setanta,
Quote:The speed of sound is not a constant, it depends upon the material through which it is transmitted.
I just have to correct this. The speed of light also depends upon the material through which it is transmitted.
The speed of light in a vacuum is a constant. Light travels slower (often considerably slower) though matter. If this weren't true, then light wouldn't be bent by glass, meaning lenses and prisms wouldn't work.