56 LABORATORY EXERCISES 



You can get a crimson light from a piece of blotting or 

 asbestos paper that has been soaked in a solution of strontium 

 chloride and then dried. 



c. In order that a color may appear red, what kind of rays 

 must be" in the light that illuminates it? What rays must a 

 light contain if we are to see an object as yellow? Why do 

 objects have these colors in sunlight? Why do colors appear 

 unnatural by electric light? 



EXERCISE 54 

 HOW SOUND IS MADE AND CARRIED 



Apparatus and Materials. Table bell or doorbell, tuning fork or 

 table fork, newspaper, watch, pillow, room with steam pipes or water 

 pipes, wooden board. 



a. While a table bell or doorbell is ringing, touch the bell 

 lightly with your finger. What proof have you that the bell 

 is vibrating? 



b. Strike a tuning fork lightly against the edge of a table, and 

 hold your finger against the fork. Account for the result. A 

 table fork can be used in the same way. Hold the fork lightly 

 by the handle while you strike the back of the prongs against 

 a table or chair, and then bring the vibrating fork near the top 

 of some loose paper, such as a partly folded newspaper. What 

 is the result, and why? 



c. Lay a watch upon a pillow, at some distance from you, 

 say, at the farther end of a table. Note whether you can hear 

 the watch, and how loud the ticking is. Then lay the watch, 

 at the same distance, upon the bare table, and compare results. 



d. Have some one scratch with a pin, or tap with a pencil, at 

 one end of a steam or water pipe, and put your ear close to the 

 other end of the pipe. Can you hear the sound? Can you 



