THE GULF STREAM. 
23. In obedience to the laws here hinted at, there is a constant 
tendency of polar waters toward the tropics and of tropical waters 
toward the poles. Captain Wilkes, of the United States Explor- 
ing Expedition, crossed one of these hyperborean under-cnrrents 
two hundred miles in breadth at the equator. 
24. Assuming the maximum velocity of the Gulf Stream at five 
knots, and its depth and breadth in the Narrows of Bernini as be- 
fore (§ 10), the vertical section across would present an area of 
two hundred millions of square feet moving at the rate of seven 
feet three inches per second. The difference of specific gravity 
between the volume of Gulf water that crosses this sectional line 
in one second, and an equal volume of water at the ocean temper- 
ature of the latitude, is fifteen millions of pounds. If these esti- 
mated dimensions (assumed merely for the purposes of illustration) 
be within limits, then the force per second operating here to pro- 
pel the waters of the Gulf toward the pole is the equilibrating ten- 
dency due to fifteen milhons of pounds of water in the latitude of 
Bernini. 
25. In investigating the currents of the seas, such agencies 
should be taken into account. As a cause, I doubt whether this 
one is sufficient of itself to produce a stream of such great velocity 
as that of the Gulf; for, assuming its estimated discharge to be 
correct, the proposition is almost susceptible of mathematical dem- 
onstration, that to overcome the resistance opposed in consequence 
of its velocity would require a force at least sufficient to drive, 
at the rate of three miles the hour, ninety thousand millions of 
tons up an inclined plane having an ascent of three inches to the 
mile.* Yet the very-principle from which this agent is derived 
is admitted to be one of the chief causes of those winds which are 
said to be the sole cause of this current. 
26. The chemical properties, or, if the expression be admissible, 
the galvanic properties of the Gulf Stream waters, as they come 
from their fountains, are different, or, rather, more intense than 
they are in sea water generally. 
In 1843 the Secretary of the Navy took measures for procur- 
ing a series of observations and experiments with regard to the 
corrosive effects of sea water upon the copper sheathing of ships. 
With patience, care, and labor, these researches were carried on 
* Supposing there be no resistance from friction. 
c 
