288 DEPARTMENT OF THE NATAL SERVICE 



500,000,000 horse-power, which agrees with the value already known from other methods 

 of calculation. 



Nothing could show more clearly than this the fundamental importance of 

 the solenoids for the origin and maintenance of the ocean currents. 



17. SUMMARY. 



Within the area of these investigations, from its boundary on the Gulf Stream 

 side to the mouth of the St. Lawrence, a number of mostly interesting phenomena 

 are encountered, which render the waters in question one of the most instructive 

 fields on the face of the globe for hydrographical and hydrodynamic research. 



Let us now glance briefly at some of the most important features. First of all, 

 there are the physical processes which take place in the boundary surface between the 

 Labrador current and the Gulf Stream occasioning the disappearance of the former, 

 with regard to these, the reader is referred to Prof. Emil Witte's clear and simple 

 treatment of the subject in the Geogr. Anzeiger, October, 1910: — ■ 



" When, on the boundary of an ocean current, warm water of high salinity 

 is brought into contact with colder water of less saline character, but having 

 approximately the same specific gravity, then the resulting mixture will, as 

 may easily be proved by the Knudsen tables, be of greater density than either 

 of its component parts. It will consequently sink down, giving rise to the 

 peculiar phenomenon known as cabbeling. 



" Obviously, this tendency in the water will likewise produce horizontal 

 currents; as the mixed water sinks down, surface water must flow in from 

 either side to take its place. By way of example, we may take the waters in 

 the vicinity of the Newfoundland bank, where the Gulf Stream encounters the 

 cold current flowing down from the Greenland seas. Throughout the wide 

 extent of the boundary surface between these two, mixed water is constantly 

 being formed, sinking down, and thus drawing in a continual further supply of 

 surface water from either side." 



It is this perpetual sinking of the water, of course, which renders the oceanic 

 boundary line here so vertical. 



Numerous pelagic organisms of slight mobility doubtless meet their death in this 

 mixture of the water, and their shells sink to the bottom. With the aid of boring 

 samples taken from the sea floor, therefore, we should probably be able to arrive at the 

 geological history of these currents. 



The water of the Gulfi Stream is more homogeneous; that of the Labrador current 

 being more in layers. In the boundary surfaces between the layers of the latter, wave 

 movements take place. These waves strike against the vertical boundary wall, giving 

 rise to submarine waves of great amplitude. In order to study these, it will be sufHcienr 

 to measure the depth of an isotherm or isohaline at the juncture of two layers. This 

 simple operation should be carried out at the same time as the hydrographical measure- 

 ments. 



Closer in towards land, the surface water of the Labrador current is driven 

 by the earth's rotation in a shoreward direction, which is one of the causes of the 

 numerous shipwrecks in the Newfoundland waters. The water pours up into the big 

 bays on the eastern shore, keeping to their north side. The greater part of the water 

 thus poured in at the surface makes its way out again as an under current, but there is, 

 as a rule, also a slight surface current in an outward direction on the southern side of 

 the bays. 



South of Newfoundland, the landward current is often perceptible far out at sea. 

 "A northerly set of 30 miles in twenty-four hours has frequently been experienced in 

 tliis neighbourhood, at times at a distance of 50 miles from the coast {vide Sailing 



