Why Are Some Things Transparent and Others Not?
Transparency is produced by the way rays of light go through substances or not. When light strikes a substance that is almost perfectly transparent, it means that the rays of light go through it almost exactly as they come in. We think quickly of glass when we think of something readily transparent. Water is almost equally as transparent. When the sunlight is shining on one side of a pane of ordinary window glass, it causes every thing on that side of the window to reflect the light which strikes it in all directions. When these rays of light strike the window pane, they go right through and that is how we are able to see the trees and grass and everything else through a clear window pane. The same reason applies also to the water.
Some kinds of window glass (the frosted kind) we cannot see through—they are not transparent. The surface of a frosted window pane is so made that when the light rays strike it the rays are twisted and broken, and do not come through as they entered the glass.
Sometimes the water is almost perfectly transparent. When water is perfectly clear, it is quite transparent. When you look at or into water that is not transparent, you will know that there are particles of solid matter floating about in it which twist and mix the light rays. If the water is not too deep you can see the bottom sometimes even when there are some particles of solid substances floating about in it, but the deeper the water the more of these solid particles there are generally in it, so that it is impossible in most waters to see the bottom if the water is deep. In some places, however, the water is so free from floating particles that the bottom of the ocean can be seen at quite considerable depths.