CHAP. VILL. } THE GULE-STREAM. 3609 
It is not easy to understand Captain Maury’s view. 
He traces all ocean currents to differences in specific 
eravitv. He says: “If we except the tides, and the 
partial currents of the sea, such as those that may he 
ereated by the wind, we may lay it down as a rule 
that all the currents of the ocean owe their origin to 
the differences of specific gravity between sea-water 
at one place and sea-water at another: for wherever 
there is such a difference, whether it be owing to dif- 
ference of temperature or to difference of saltness, 
&e., it is a difference that disturbs equilibrium, and 
currents are the consequence.” ' These differences 
in specifie gravity he attributes to two principal 
causes ; differences in temperature, and excess of salts 
produced by evaporation. Captain Maury explains 
his views as to the first of these causes by an illustra- 
tion. ‘Let us now suppose that all the water within 
the tropics to the depth of one hundred fathoms sud- 
denly becomes oil. The aqueous equilibrium of the 
planet would thereby be disturbed, and a general 
system of currents and counter-currents would be 
immediately commenced, the oil in an unbroken sheet 
on the surface running towards the poles, and the 
water as an under-current towards the equator. The 
oil is supposed, as it reaches the polar basin, to be re- 
converted into water, and the water te become oil as 
it erosses Cancer and Capricorn, rising to the surface 
in intertropical regions, and returning as_ before.” 
«Now, do not the cold water of the north, and the 
warm water of the gulf made specifically lighter by 
tropical heat, and which we see actually presenting 
The Physical Geography of the Sea, and its Meteorology. By 
Mf. Maury, LL.D: 
