Cup and Shilling

“The refraction of water is beautifully proved by the following simple experiment. Place an empty cup, with a shilling on the bottom, in such a position that the side of the cup will just hide the piece of money from the eye. Then let another person fill the cup with water, keeping the eye in the same position as before. As the water is poured in, the shilling will be come visible, appearing to rise with the water. The effect of the water is to bend the ray of light coming from the shilling, so as to make it meet the eye below the point where it otherwise would. Thus the eye could not see the shilling in the direction of c, since the line, of vision is towards a, and c is hidden by the side of the cup. But the refraction of the water bends the way downwards, producing the same effect as though the object had been raised upwards, and hence it becomes visible.” —Comstock, 1850

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