( 294 ) 



III —THE CURRENTS. 



(236.) General Remarks. — A Current is to be unaerstood as a stream 

 on, or a particular set in the direction of, the surface of the sea, occa- 

 sioned by Winds and other impulses, exclusive of (but which may be 

 influenced by) the causes of the Tides. It is an observation of Dampier, 

 that Currents are scarcely ever felt but at sea, and Tides only upon the 

 coasts ; and it certainly is an established fact that Currents prevail mostly 

 in those parts where the Tides are weak and scarcely perceptible, or where 

 the sea, apparently little influenced by the causes of the Tides, is disposed 

 to a quiescent state. This will be obvious by an attentive consideration 

 of the following descriptions. The necessity of attention to the silent, 

 imperceptible, and therefore dangerous operation of Currents, vnll be 

 equally apparent. 



(237.) The usual method of estimating the existence, direction, and 

 velocity of a Current, is the comparison between the observed position of 

 a ship and that obtained by dead-reckoning. It may be as well to observe 

 in the outset, that this method of observation involves some amount of 

 fallacy, as a Current will be the general receiver of all errors or imper- 

 fections of observation, and beyond doubt the strength of Currents has 

 been frequently exaggerated from this very cause. Now, as the latitude 

 is attained far more easily and accurately than the longitude, it follows 

 that this exaggeration has been chiefly shown in those Currents supposed 

 to move to East and "West. Still, by combining a large number of obser- 

 vations, we may safely conclude that they will neutralize each other's 

 errors, and afford something like an accurate conclusion. 



(2.38.) An excellent repository of a vast number of early Current obser- 

 vations is found in the elaborate charts of Major Eennell, a great mine for 

 facts in surface Current theory. Commander Maury's charts, and the more 

 recent ones of our own and other Meteorological Offices, likewise alibrd a 

 great addition to our stock of knowledge. This is also increased by 

 numerous detached observations scattered through many works. All these, 

 as far as attainable, were integrated at a great expenditure of labour, in 

 the Chart of the North Atlantic Ocean, published by Mr. Laurie, which 

 this work particularly elucidates. 



(239.) But since that chart was constructed, a much more extensive 

 series of observations has been incorporated with those just named, in a 

 set of charts, one for each month of the year, pubhshed by the Meteorolo- 

 gical Office in 1872. They were contained in the first 800 registers col- 

 lected by that office, and were reduced by Mr. R. Strachan. In addition 

 to these registers, the whole of the available data in Eennell's and Maury's 

 charts were integrated with them, and thus gave a far more perfect view 

 of the Atlantic Currents, between the Equator and 40° N., and from the 

 African coast to the Gulf of Mexico, than was before attainable. A portion 

 of the information then collected was shown by Admiral FitzRoy, in 1859, 

 on the Wind Charts published by the Meteorological Department, which 



