SOUND 65 



Many determinations of this kind have been made since 

 those of Roemer, and it has been found that he was some- 

 what in error, as the time required by light in traveling 

 across the earth's orbit is about 16 minutes and 40 seconds, 

 or 1000 seconds. Since the diameter of the earth's orbit 

 is about 186,000,000 miles the speed of light must be 

 about 186,000 miles per second. Determinations of the 

 speed of light have been made in several other ways with 

 almost like results. 



34. Theories Concerning Light. Although it is very easy 

 to perceive light and to examine many of its properties, 

 yet to determine just what it is that produces the light 

 sensation has been found vastly difficult. Sir Isaac New- 

 ton thought that light consisted of streams of very mi- 

 nute particles, or corpuscles, thrown off by the luminous 

 body. Since about 1800, it has been considered a form 

 of wave motion which is transmitted through the ether 

 which fills all space. 



35. Sound. Experiment 34. Arrange a large wide- 

 mouthed bottle with a small bell suspended in it from 

 the stopper and a delivery tube extending through the 

 stopper. Attach the delivery tube by a thick- walled 

 rubber tube to an air pump and exhaust the air from 

 the bottle. Shake the bottle so that the bell can be 

 seen to ring but does not strike the sides of the bottle. 



Can the sound be heard distinctly ? Fig. 39. 



Although sound is not related to the sun's energy it 

 seems best for certain reasons to consider it briefly in this 

 place. In Experiment 34, it was found that if the air 

 was exhausted and the bell did not touch the sides of 

 the bottle, almost no sound was heard when the clapper 

 of the bell showed that the bell was ringing. This shows 

 that the sounds we usually hear are transmitted in some 

 way by the aid of the air. 



