THE NEW WORLD OF SCIENCE 



device are situated at Mj, M 2 and M 3 and if, for example G M x 

 be 3370 meters, the sound of the gun will reach Mj in 10 sec- 

 onds, and the front of the spherical wave will go through M , 

 N 2 and N 8 . This wave front moving with the velocity of 337 

 meters per second will reach M 2 later than it reaches M t . 

 How much later is determined by the time it takes the sound 



N M 

 to travel the distance N 2 M 2 (that is by - -seconds). Thus 



oo/ 



\ 1 *? 



\l 



*/ 



|A 3 



A 



/' 



Figure i 

 the interval between the arrival of the sound at M t and at M a 



will be 



337 



seconds and the interval between the arrival at 



! and at M 3 will be - - seconds. Suppose the distance 



N 2 M 2 were 33.7 meters, then the interval of time between the 

 arrival at M x and at M 2 would be one-tenth of a second and 



