INTERMINGLING OF UNDULATIONS. 



TI1E DUCKS ON THE LAKE. 



what is the experiment that the ducks are going to per- 

 form?" 



" It is an experiment on the crossing of undulations" 

 said Lawrence. "You see these ducks are swimming about 

 in all directions, and each one, as he parts the water with 

 his breast and his paddling legs, makes two lines of waves, 

 or undulations, which diverge from each other as they re- 

 cede behind him, or, rather, as he advances and leaves 

 them. There is something very curious in the laws of 

 motion that govern the formation and the spread of these 

 lines; but I am not going to say any thing about that 

 now, but only to have you see what the effect is when two 

 of these lines of waves cross each other. You -would think, 

 in such a case, that they would disturb and destroy each 

 other, as one would suppose the undulations or vibrations 

 of light would do. But you will see, when we get a good 

 chance that is, Avhen two ducks happen to come along 

 side by side, so that the lines of waves cross each other 

 that there is much less interference than one would sup- 



