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THE POPULAR SCIENCE MONTHLY. 



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 down- 

 ward 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 oft' 

 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 witli 

 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 tbe water and stir them together. Throw the beam of 

 light down once more. This is indeed remarkable. The tumbler of inilk-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." 



Vui. 5. Experiment showing the Law of Eefraction. 



By the following simple contrivance, illustrated in Fig. 5, Dr. Mayer 

 shows the pupil how he can demonstrate the law of the refraction of 



