OUTLINES OF NATURAL PHILOSOPHY. 



were most elevated, have become most depress- 

 ed. 



The alternate elevations and depressions thus produced 

 are called waves. 



The water in the formation of waves has a vibratory 

 or reciprocating motion, both in a horizontal and 

 a vertical direction, by which it passes from the 

 columns that are shortened to those that are length- 

 ened, and returns again in the opposite direction. 

 Progressive motion is not necessary to undula- 

 tion. 



302. The vibrations of water in the form of 

 waves, may be compared to the reciprocations of 

 the same fluid in a syphon or bent tube ; and it 

 was from this that NEWTON deduced the velocity 

 of waves, and the time required to an undula- 

 tion. 



The time of an undulation, is the time from the wave 

 being highest at any point, to its being highest at 

 that point again. The velocity of the wave is the 

 rate at which the points of greatest elevation or de- 

 pression seem to change their places. 



303. If a be the altitude of a wave, b half the 

 breadth, * the circumference of the circle, of 

 which the diameter is 1, the time of an undula- 



tion 



