What have you done in this case? You answer at once that you have bent the sunlight out of its course and turned it in another direction. If the glass were not there it would fall in a straight line on the window seat. This bending out of the straight line is called reflection.

Now for an experiment; cut a small round piece of cork, not quite half an inch thick. Run a needle into its center and place it in a tumbler two-thirds full of water, needle downwards.

Looking down on the cork you cannot see the needle. Now alter your position, and stoop down so that your eye is on level with the table on which the glass stands. Then you will perceive the needle to be on the top of the cork.

This apparent topsy-turveydom is called total reflection. The needle is reflected on the top of the water, and as the ray from your eye meets the top of the water, you see the needle, as it were, on the top of the cork.