CHAP. VIII.] THE GULF-STREAM. 365 



It is not easy to understand Captain Maury's view. 

 He traces all ocean currents to differences in specific 

 gravity. He says : " If we except the tides, and the 

 partial currents of the sea, such as those that may be 

 created 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, 

 &c., it is a difference that disturbs equilibrium, and 

 currents are the consequence."^ These differences 

 in specific 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 to become oil as 

 it crosses 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 

 ^l T. Maury, LL.D. 



