Page:Popular Science Monthly Volume 11.djvu/682

662 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:



By the following simple contrivance, illustrated in Fig. 5, Dr. Mayer shows the pupil how he can demonstrate the law of the refraction of