1910] McEwen: Preliminary Hydrographic "Report. 201 



depth below which the effect of the wind is practically negligible, 



11 t ,i <<-■-. -i ,•/.,, ^ ~-6 meters 



is called the Keibungstiefe. D meters = — // — , 



V sin seconds 

 where D is the "Reibungstiefe," the geographical latitude, and 

 h is the wind-velocity. It is to be understood that the depth of 

 the water exceeds I), and that the value of is not less than 

 about 2°. If the depth is less than I), the deflection of the 

 current from the direction of the wind is less and as the depth 

 diminishes the effect of the earth's rotation diminishes, though 

 it is only when the depth is less than i D that the above state- 

 ments are uo1 approximately true. If. where the latitude is 30°, 



the wind-velocity is 15 ^ — , D equals forty fathoms. 



hour 



The average velocity in such a surface stream is such that 

 the total quantity of water transported is zero in a direction 

 parallel to the wind and is a maximum in a direction 90° to the 

 right of the wind. 



From this theory the component of the wind-velocity perpen- 

 dicular to the coast would produce currents parallel to the coast, 

 the direction of the currents being, for the California and Mex- 

 ican coasts, towards the south when the wind blows from the 

 west, towards the north when the wind blows from the east. 

 Also the component of the wind-velocity parallel to the coast 

 would produce currents running towards or away from the coast 

 according as the direction of the wind is from south to north 

 or north to south. In the latter case, which is true during Hie 

 summer, the water for a depth of about forty fathoms would 

 be flowing away from the coast because of the effect of the wind 

 and earth's rotation, and the removal of this layer would cause 

 an upwelling of the deeper and colder water to take its place. 



In the winter, when the prevailing winds are nearly perpen- 

 dicular to the coast, the currents would be parallel to the coast 

 and no upwelling of the colder water would take place. 



THE PROPERTIES OP THE WATER OF SAX DIEGO BAY. 



From June 13 to July 18, 1908, fourteen observations of 

 temperature and density were taken. The following- table gives 

 a series of values from the entrance to the bay to National City : 



