190 



THE STORY-BOOK OF SCIENCE 



after all, in comparison with the inconceivable veloc- 

 ity of light. 



' * The unequal rapidity with which sound and light 

 travel accounts for the following fact. From a dis- 

 tance a wood-cutter is seen chopping wood, or a 

 mason cutting stone. We see the ax strike the wood, 

 the mallet tap the stone, and some time after we 

 hear the sound." 



"One Sunday be- 

 fore church," interposed 

 Jules, "I was watching 

 from a distance the ring- 

 ing of the bell. I saw 

 the tongue strike and the 

 sound did not come until 

 later. Now I see the rea- 

 son." 



"If you count the num- 

 ber of seconds between 

 the appearance of the 

 flash and the instant the 

 Bells Ringing thunder begins to be 



heard, you can tell what distance you are from the 

 storm-cloud. ' ' 



"Is a second very long?" Emile asked. 

 "It is about the length of one beat of the pulse. 

 All we have to do, then, is to count, one, two, three, 

 four, etc., without haste, but not too slowly, to have 

 about the number of seconds. Note the instant the 

 flash lights up the stormy cumulus, and count slowly 

 until you hear the thunder." 



With watchful eye and attentive ear all began 



