EFFECTS OF CURRENTS UPON NA VIGATION. 33 



his port, perhaps to be as rudely driven back again. But 

 each breathing spell renews his energies, until at last he 

 may enter his haven in safety, though many, in this terrible 

 •contest, may sink to rise no more 



Other currents as well as the Gulf Stream materially af- 

 fect navigation. While an intimate knowledge of them is 

 necessary, in order to avoid the danger of mistaking the 

 true position of a vessel, its progress to port may be facili- 

 tated by falling in with a local stream, or steering clear of 

 it, according as its direction is favorable or adverse. 



The effect of currents was perceived long before anything 

 was known of their direction and velocity, and Columbus 

 was strengthened in his belief that land might be reached 

 across the Atlantic westward, by substances which had 

 drifted from that quarter. After the commencement of his 

 great undertaking, when, day after day, nothing had been 

 seen but a shoreless horizon, and hope had nearly expired 

 in his own breast, while his crew were on the verge of open 

 rebellion, the effect of the oceanic currents restored his con- 

 fidence and allayed their clamors. A branch of thorn, with 

 berries on it, appeared ; a reed was picked up, and a staff 

 artificially carved — intimations that an inhabited land lay 

 before the adventurers, which was at length revealed to their 

 gaze, and terminated forever the mystery which had rested 

 upon the western flood. 



A Tide is a wave of the whole ocean, which is elevated 

 to a certain height, and then sinks after the manner of a 

 common wave. The interval between the two positions 

 forms the tide. The principal cause is the attraction of the 

 sun and moon, the latter being the more potent agent. The 

 sea rises or flows, as it is called, by degrees, about six hours ; 

 it remains stationary about a quarter of an hour ; and then 

 retires or ebbs during another six hours, to flow again after 

 a brief repose. Thus every day, or the period elapsing 

 between successive returns of the moon to the meridian of a 



