THE VELOCITY OF WAVES. 



765 



third than that found in river water. It varies from a fifth to 

 a thirtieth, and gradually increases from the surface to a depth 

 of about three hundred and twenty-five to three hundred and 

 eighty fathoms. The uniformity in the constitution of the 

 waters of the sea is chiefly caused by the action of the waves / 

 which finally mix and mingle the waters into a homogenious 

 mass. The waves of the sea are caused chiefly by the action 

 of the wind, and the effect continues even after the wind has 

 ceased. One of the grandest spectacles at sea is offered by the 

 regular movement of the waves in perfectly calm weather, 

 when not a breath of air stirs the sails. During to the Au- 

 tumnal calm under the Tropic of Cancer, these waves appear 

 with astonishing regularity at intervals of two hundred to 

 three hundred yards, sweep under the ship, and as far as the 

 eye can reach, are seen advancing and passing away, as regu 

 hrly as the furrows in a field. Such waves are caused by th'\ 

 regularity of the trade winds. The height of the waves in 

 not the same in all seas. It is greater where the basin r 

 deeper in proportion to the surface, and also as the water v 

 h esher and yields easier to the impulses of the wind. 



The height of waves has been variously measured. Some 

 observers have claimed to see them over one hundred feet 

 high, but from twenty to fifty feet is about the average of 

 observations on the Atlantic. The breadth of a wave is cal 

 (f ulated as fifteen times its height. Thus, a wave four feet high 

 is sixty feet broad. The inclination of the sides of the waves 

 varies however with the force of the wind, and with the 

 strength of the secondary vibrations in the water, which may 

 interfere with the primary ones. The speed of the waves is 

 only apparent like the motion in a length of cloth shaken rp 

 and down. Floating objects do not change their relative posi- 

 tions, but slowly, except in rising and falling with the wave 

 The real movement of the sea is that of a drifting current, 

 which is slowly formed under the action of the wind, and this 



