hand-mirror. Now set fire to a small bit of paper, and drop it into the jar. When it is burned out, put the postal-card in place, and the vessel will be filled with smoke. The beam that is reflected downward from the mirror enters the slit, and you see a slender ribbon of light extending downward through the jar, while all around it is quite dark and black. Fig. 4 shows the light streaming through the opening in the card, and lighting up the particles of smoke in its path. Take off the card, and let the reflected beam fall freely into the jar: the smoke is now wholly illuminated, and the vessel appears to be full of light
To make a milk-and-water lamp:
"Take away the jar and put a clean glass tumbler in its place. Fill this with water and throw the beam of reflected light down upon it, and the water will be lighted up so that we can easily see the tumbler in the dark. Now add a teaspoonful of milk to the water and stir them together. Throw the beam of light down once more. This is indeed remarkable. The tumbler of milk-and-water shines like a lamp, and lights up the room so that we can easily see to read by its strange white light. Move the mirror and turn aside the beam of light, and instantly the room becomes dark. Turn the light back again, and once more the glass is full of light. Here the minute particles of milk floating in the water catch and reflect the light in every direction, so that the entire goblet seems filled with it, and the room is lighted up by the strange reflections that shine through the glass."
Fig. 5.—Experiment showing the Law of Refraction.
By the following simple contrivance, illustrated in Fig. 5, Dr. Mayer shows the pupil how he can demonstrate the law of the refraction of
