THE VELOCITY OF SOUND 191 



the observation. Finally a flash was seen. They 

 counted, the uncle beating time. One two three 

 four five At twelve came the thunder, but so 

 faint that they could only just hear it. 



"It took twelve seconds for the sound of the thun- 

 der to reach us, ' ' said Uncle Paul. * * From what dis- 

 tance does it come, if sound travels 340 meters a sec- 

 ond!" 



"You must multiply 340 by twelve, " replied 

 Claire. 



"Well, Miss, doit.' ' 



Claire made the calculation. The result was 4080 

 meters. 



"The flash of lightning was 4080 meters away; we 

 are more than a league from the storm-cloud, " said 

 her uncle. 



"How easy that is!" exclaimed Emile. "You 

 count one, two, three, four, and without moving you 

 know how far away the thunderbolt has just f alien. " 



"The longer the time between the flash and the 

 noise, the farther away is the cloud. When the re- 

 port comes at the same time as the flash, the explo- 

 sion is quite near. Jules knows that well since the 

 day of the storm in the pine woods. " 



"I have heard that there is no longer any danger 

 after the lightning is seen," said Claire. 



"A thunderbolt is as rapid as light. An electric 

 <-\ plosion is, therefore, ended as soon as the flash 

 appears, and all danger is then passed ; for the thun- 

 der, however loud it may be, can do no harm." 



