The Mighty Deep 



tends to drag on the layer just below, which 

 again affects the one lower still. By influence 

 thus exerted and passed from one to another, the 

 result of a long-continued wind-pressure in one 

 direction is to set going powerful streams, which 

 in the first instance were due chiefly or only to 

 wind. 



Round the Earth, where fairly open sea permits 

 them to develop, are two wide belts of very per- 

 sistent winds the Trades which remain prac- 

 tically the same all the year round ; only shifting 

 their limits with the changing seasons. 



They blow from the north-east and from the 

 south-east slanting towards the equator. So, 

 speaking roughly, they are easterly winds travel- 

 ling towards the west. As a consequence of their 

 steady pressure, we have the great Equatorial 

 Current of the tropics, pouring from east to west 

 in two halves, north and south of the equator. 

 This vast ocean-river, started and kept going by 

 the trade-winds, has been described in the more 

 important part of its course as a " magnificent 

 surface-current of hot water, four thousand miles 

 long by four hundred and fifty broad," moving 

 "at an average rate of thirty miles a day" and, 

 it may be added, at least over six hundred feet 

 in depth. 



64 



