2l6 ANSWERS TO PRACTICAL QUESTIONS 



It is produced by the vibration of the wires. These 

 are thrown into motion by the wind and other causes. 



23. Why will a variation in the quantity of water in the 

 goblet, when caused to sound as in the experiment described 

 on page 123, make a difference in the tone / 



It changes the length of the vibrating portion of the 

 glass. 



24. At what rate (in metres) will sound move through 

 air at 20 CJ 



Sound moves at the rate of 1,090 feet at o C. The 

 difference is nearly 2 feet for each degree C. 



1090 feet + 40 feet =1130 feet. 



OPTICS. 



177. 1-25. (See Key, pp. 35-39.) 



26. What is the principle of the kaleidoscope? 



27. Which will be seen at the greater distance, a yellow 

 or a gray body ? 



The yellow, since it is brighter. 



28. Look down into the glass of water shown in fig. 145, 

 and at a certain angle you will see two spoons, one small 

 and having the real handle of the spoon, though apparently 

 bent, and the real spoon with no handle. Explain. 



In trying the experiments here alluded to, the glass 

 should be looked into at all possible angles, and the 

 spoon be turned about in the goblet. The glass of water 

 acts as a convex lens to magnify objects ; the concave 



