Geograph - photograph every grid square

This post, which someone has "thoughfully" discarded in the Bury, Bolton and Manchester Canal, exempifies two of the remarkable properties of light which as many people will tell you, "only travels in a straight line".

Below the waterline, are two images of the post. The stronger image to the right is the reflection which we are used to seeing. The other "image" is the actual post which appears to bend dramatically where it enters/leaves the water. The post is, of course, straight. The bending is an optical illusion caused by the light travelling at different speeds in different media (in this case water and air). A phenomenon known as refraction.

see Link (Archive Link ) for a diagrammatic representation of reflection and refraction.