80 INTERMINGLING OF UNDULATIONS. 



his chair. "I'll certainly do it ; I'd as lief go second ciasa 

 as not." 



"Very well," said Lawrence. "But now look at the 

 ducks; there are two coming now directly before us in 

 just the right position." 



The two ducks that Lawrence referred to were twin* 

 ming along nearly side by side, at a short distance from 

 the shore, and the little line of waves which passed off 

 from the left side of one crossed that which came from 

 the right side of the other, but the two lines seemed 

 scarcely to interfere with each other at all. They ap- 

 peared to go on after the crossing, each on its way, as if 

 it had been very little disturbed by the other. 



This is only one among the innumerable cases occurring 

 in nature which show the possibility of the coexistence of 

 different vibrations among the same set of particles that 

 is, in the same substance with a degree of independence 

 of each other which, without proof from experiment, we 

 should have thought impossible. John was very much 

 surprised to see how little disturbed the diverging lines 

 of waves made by the two ducks were in crossing each 

 other. It is true that afterward, when he saw several 

 ducks swimming this way and that, in all directions, a 

 good deal of irregular commotion was produced on the 

 surface of the water ; but this apparent confusion seemed 

 to be caused quite as much by the difficulty of following 

 with the eye, and separating by the mind, all the differ- 

 ent lines, as by any actual interference in the undulatory 

 actions. 



The case of different sounds coming through the air to 

 the ear, which has already been referred to, is another in- 

 stance of the coexistence of different vibrations in the 

 same substance, each preserving unimpaired its own dis- 

 tinctive character. So, when a bell is struck especially 



