THE TIDES 



THE last chapter was entirely devoted to a cursory 

 consideration of the oceanic currents as distinguished 

 from the regular ebb and flow of the tides. And an 

 attempt was made to explain the difference between 

 current and tide, a very lame one, I fear, for most 

 people cannot help confusing the two, being indeed 

 satisfied to denominate the movement of any body of 

 water in any given direction a current, without any 

 regard to the cause of its movement. But because to 

 the general public the distinction between tide and 

 current is exceedingly hazy, I hope I may be forgiven 

 for again endeavouring to make the difference clear, 

 not this time by a lame simile, but by an exceedingly 

 brief recital of the actual facts concerning each. 

 Current is the movement of a body of water produced 

 by a difference in specific gravity caused by a difference 

 of temperature, or change in salinity, or evaporation, 

 or the drag of the wind along the surface. It is 

 always more or less local, and in several well-marked 

 cases it is nearly permanent in speed and direction. 

 Tide, on the other hand, is caused by the action of the 

 moon and, in a lesser degree, of the sun upon the 

 great skin of water covering two-thirds of the surface 

 of the globe. Four times in each day of twenty-four 

 hours the drawing power of gravity exerted by these 



Hi 



