"As in water face answereth to face, so the heart of man to man."—Proverbs xxvii.
507. Does glass obstruct the passage of any portion of light?
Glass reflects (sends back) a very small portion of light. This may be observed by holding a piece of paper, or a hand, a few inches from a window, when a faint reflection of it will be visible. Probably the small amount of light reflected by transparent glass, which gives a passage to the greater part of the rays, may serve to illustrate the small amount of light reflected from black surfaces, which absorbs the greater portion of light.
Instead of a piece of white paper, hold a piece of black cloth two or three inches from the window-pane, and you will have two reflections so weak that the image of the cloth will be almost lost. The first reflection is that of the very small amount of light from the black surface on to the glass, and the second reflection is that of the inconceivably small amount returned by the glass, and by which the faint image of the black cloth is produced. But put the black cloth outside of the window-pane, and then hold an object before them, and you will find that the two weak reflectors, acting together, produce an improved image, or reflection.
508. Why, if a book is held between a candle-light and the wall, does a shadow fall upon the wall?
Because the rays of light are intercepted by the book.
509. Why do the rays pass over the edges of the book in a direct line with the flame of the candle?
Because light always travels in straight lines.