IS THE GULF STREAM A MYTH? 129 



evidence that the action of the sun results in making 

 the water lighter. 



Now, Maury says that the water thus lightened 

 must flow over and form a surface-current towards the 

 Poles ; while the cold and heavy water from the polar 

 seas, as soon as it reaches the temperate zone, must 

 sink and form a submarine current. He recognises in 

 these facts the mainspring of the whole system of 

 oceanic circulation. If a long trough be divided into 

 two compartments, and we fill one with oil and the 

 other with water, and then remove the dividing plate, 

 we shall see the oil rushing over the water at one end 

 of the trough, and the water rushing under the oil at 

 the other. And if we further conceive that oil is con- 

 tinually being added at that end of the trough origi- 

 nally filled with oil, while water is continually added 

 at the other, it is clear that the system of currents 

 would continue in action : that is, there would be a 

 continual flow of oil in one direction along the surface 

 of the water, and of water in the contrary direction 

 underneath the oil. 



But Sir John Herschel maintains that no such effects 

 as Maury describes could follow the action of the sun's 

 heat upon the equatorial waters. He argues thus: 

 Granting that these waters become lighter and expand 

 in volume, yet they can only move upwards, down- 

 wards, or sideways. There can be nothing to cause 

 either of the two first forms of motion; and as for 

 motion sideways, it can only result from the gradual 

 slope caused by the bulging of the equatorial waters. 



K 



