SCIENCE OF COMMON THINGS. 



What is a sonorous body ? Sonorous vibrations. Bell metal. 



Why does a bell rung in a receiver exhausted of air fail to produce 

 sound ? 



Because no air is present to receive and transmit the 

 vibrations. 



7*37* What is a sounding or sonorous body f 



A body possessing both hardness and elasticity, 

 which, when struck, vibrates, and imparts to the air in 

 contact with it undulations corresponding to its vibra- 



tions. 



7*38 Why has the peculiar kind of motion in bodies which gives rise to 

 the sensation of sound, been termed vibration ? 



Because a striking analogy may be traced between 

 the tremulous agitation which takes place among the 

 particles of a sounding body and the oscillations of a 

 pendulum. 



7*30 How 'may the nature of sonorous 

 vibrations be illustrated f 



By noticing the visible mo- 

 tions which occur on striking 

 or twitching a tightly extender 

 cord or wire. Suppose such a 

 cord, represented by the cen- Flg 31 



tral line in Fig. 31, to be 



forcibly drawn out to A, and let go ; it would immedi- 

 ately recover its original position by virtue of its elas- 

 ticity ; but when it reached the central point, it would 

 have acquired so much momentum as would cause it to 

 pass onward to a ; thence it would vibrate back in the 

 same manner to B, and back again to 5, the extent of 

 its vibration being gradually diminished by the resist- 

 ance of the air, so that it would at length return to a 

 state of rest. 



7*30 Why are copper and iron sonorous, and not lead ? 



Copper and iron are hard and elastic / but as lead 

 is neither hard nor elastic, it is not sonorous. 



731 Of what is bell-metal made f 



Of copper and tin in the following proportions : In 

 every five pounds of bell-metal there should be one 

 pound of tin and four pounds of copper. 



