Re: Why can you still see a perfectly transparent piece of glass in water?

When a ray of light traveling through a transparent medium encounters a 
boundary leading into another transparent medium, part of the ray is 
reflected and the other enters the second medium.  The ray that enters the 
second medium is bent at the boundary and is said to be refracted.  The 
reflected ray and refracted ray all lie in the same plane. 

The piece of glass is not perfectly transparent. You are seeing reflected 
light from the piece of glass.  Much of the light is allowed to pass 
through the glass unhindered. The concept of refraction, bending light, 
also plays a role thus distorting the objects perceived position and size 
in the water.  Your ability to see an object is proportional to the amount 
of light that is reflected or refracted.

You may want to consult a general physics book for further explanation.

Good Luck!
Jared

[Moderator note:  You might want to try a fun experiment.  All it takes is a 
bowl with clear vegtable oil and some small glass objects that can be immersed 
in the bowl of oil.  The type of glass that works best for me is called Pyrex. 
Try to notice how easy or hard it is to see the glass when it is under the 
surface of the oil.]