SUPPLEMENTARY RULES. 



6l 



of floating objects, such as foam, seaweed, wood, etc., are collected in this line. 

 Such lines are seen on a small scale near the shores when the wind is directed against 

 the land. They then run parallel to the shore, often only like an oily band, marking 

 the limit between the somewhat brackish water near the shore and the more salt 

 water outside. Mr. Sandstrom has investigated directly the motion in the neigh- 

 borhood of this line and found horizontal and vertical motion to be that represented 

 by fig. 55.* Under the same condition of wind against the coast these lines exist 

 on greater scale several kilometers from the coast, separating the coast-water from 

 the salter sea- water. They are very well known by the fishermen, especially on 

 account of the danger to the nets when they are set out across the line. These lines 

 may also be seen under favorable circumstances on the open ocean, separating 

 sea-currents of opposite directions. f 



B 



Fig. 55. Line of convergence at sea. 



A. Motion at sea's surface. B. Motion in a vertical section. 



The investigation of these lines, their course, the degree of their constancy, etc., 

 may be of great use for the kinematic investigation of the oceans. 



139. Dynamic Diagnosis of Motion in the Free Space. The observations of 

 the air-motion in the higher strata are still too scarce to form the basis of a satis- 

 factory construction of the motions, if only direct kinematic methods should be 

 used. The arrows on the charts are far too few to determine the course of the lines 

 of flow, and the numbers added to them are too few to determine the course of the 

 lines of equal wind-intensity. We can not therefore avoid relying upon dynamic 

 principles, if in such a case as this we should be able to give a fairly probable recon- 

 struction of the air-motion on this occasion. 



*J. W. Sandstrom: Windstrome in Gullmarfjord. Svenska Hydrografisk-biologiska Kommissionens Skrifter II. 



fAlthough the phenomenon must often have been observed, not only near the coasts, but also in the open sea, 

 I have not been able to find any reference to it in literature in the latter case. I am indebted to Professor Fridtjof 

 Nansen for the following communication concerning this case: 



"Lines of convergence, as you mention, are frequently met with in the open sea, wherever a surface-current 

 formed by light surface-water meets with another current formed by heavier water. Such conditions are quite com- 

 mon along the margin of the East-Greenland Polar Current. I remember especially to have observed such a remarkably 

 distinct line of convergence in the Denmark Strait, northwest of Iceland, in about 6642' N. Lat. and 26 40' W. Long, 

 where we were with the 'Michael Sars' on August 3, 1900. The cold but light surface-water of the Polar Current 

 met here with the warmer but more saline and consequently heavier water of the Irminger Current, coming from the 

 south. One could distinctly see how the latter water flowed in under the surface-layer of polar water, and everything 

 floating on its surface was, as it were, skimmed off by the polar water, especially of course all kinds of foam, and the 

 line of convergence between the two currents was consequently marked with quantities of this foam which had been 

 skimmed off, and we could thus easily trace the line across the sea surface, as far as the eye could reach toward the 

 horizon, both northeastward and southwest ward." 



