GENERAL DESCRIPTION. 299 



they cease altogether, or become imperceptible to ordinary means of 

 measurement. This has been found to be eminently the case in the expe- 

 rience gained in laying submarine telegraph cables. If the motion of the 

 surface water were continued to any great depth, or if there were change- 

 able and varying sub-surface streams, it would very greatly interfere with 

 the success of these enterprises, but no such obstacles have shown them- 

 selves to be of any magnitude. 



(250.) Of Currents there are two distinctions : — 1. The Drift Current ; 

 2. The Stream Current. 



The Drift, or Drift Current, is the mere effect of a constant or very pre- 

 valent Wind on the surface water, impelling it to leeward until it meets 

 with some obstacle which stops it, and occasions an accumulation and 

 consequent Stream of Current. It matters not whether the obstacle be 

 land or banks, or a Stream of Current already formed. The Drift Current 

 is generally shallow, and at a mean, perhaps, of no more than half a mile 

 an hour, when the wind is constant and a good breeze. Such a Current, 

 from a predominance of Westerly winds, occupies the Northern region of 

 the North Atlantic, from the N.W. and West to the E.N.E. and S.E. ; 

 and such, likewise, is that occupying the central portion of the Ocean under 

 the influence of the Trade Winds. 



The Stream Current is formed by the accumulated waters of a Drift 

 Current. It is more limited, but it may be of any bulk, or depth, or 

 velocity. Of such is the temporary stream setting at times from the Bay 

 of Biscay to the West of Ireland ; and of such is the Crulf Streavn, setting 

 from the Mexican Sea to the Banks of Newfoundland, and terminating to 

 the West of the Azores. 



In some parts the Current is compounded of Drift and Stream ; for a 

 Stream, already formed, may pass through the region of a prevalent wind, 

 in a direction according with that of its Drift Current, and receive an 

 acceleration of motion from it accordingly. Of such are the Equatorial 

 Currents, which will be presently noticed. 



(251.) The illustrative chart at the commencement of this section, page 

 295, will best explain the general Current system of the North Atlantic 

 Ocean. Although this gives the mean of all observations throughout the 

 year, and therefore would require considerable modilication in various 

 parts, if it were made to show what is to be expected at any special time 

 or season, yet it will correctly represent that circulatory system which is 

 found to be common to all the Oceans. 



There appear to be two gyrations of the water of the North Atlantic 

 Ocean. Around a central area, crossed by the parallel of 30° N. latitude, 

 and termed the Sargasso Sea, the whole of the water between lat. 10° N. 

 and 42° or 43° N., limits varying with the seasons, revolves against the 

 apparent course of the sun. To the North of this, a portion of the water 

 is deflected to the N.E., and revolves around some point not very far from 

 Iceland, though some have considered that, after circulating around the 

 Arctic basin, it re-enters the area on the West. 



As the meteorological Equator, or the division between the phenomena 

 of the Northern and Southern Hemispheres, lies to the North of the 

 terrestrial Equator, we find that a reverse current, of varying magnitude 



