IV- 38 



Astoria, where the winds are blowing off the Pacific 

 Ocean, there are 76 inches of precipitation, including 

 4 inches of snow. At Portland the prevailing winds 

 blow off the continental land mass and there are 43 

 inches of precipitation, but 72 inches of snow. 



TIDE 



The tide stands alone as a controlling force in the estuarine envi- 

 ronment. The ebb and flow of the tide are the great facts of the 

 estuarine zone, and have determined much of man's history from the 

 time Julius Caesar lost a fleet because of the tides in the English 

 channel to the time of D-Day in 1944, which was set because of the 

 right combination of tide and moon. 



Tides are easily understood. The sun, the moon, and the earth 

 mutually attract each other, according to Newton's law of gravita- 

 tion*; the great masses of fluid in the ocean, being more sensitive 

 to tiny changes in gravitation force than the solid land, are pulled 

 about rather freely in a predictable fashion based on the relative 

 positions of sun, moon, and earth. They are predictable to such 

 an extent that tables of accurate predictions of tidal height are 



*It is interesting to note that observations of the rhythmic rise 

 and fall of the tide led to the mathematical concepts through 

 which the law was formulated. 



