37 



porary boundary waves and vortex movements be disassociated from 

 a representative picture of prevailing conditions, (cf . Helland-Hansen 

 and Nansen, "The Norwegian Sea," Bergen, 1909.) To such an 

 end the dynamic features of modern physical oceanography are best 

 carried out by several craft cooperating in one systematic program of 

 investigation, which may or may not extend over great expanses of 

 the ocean. Here is an important requirement which would appear 

 to demand certain revisions in the program of expeditions, which in 

 the past have usually been performed by one vessel sailing under a 

 more or less roving commission. These modern methods in dynamic 



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Fig. 18. — A series of station lines radiating from the Grand Banks is an example of the correct methods 

 to employ in order to obtain the best collection of material leading to an investigation of the currents 

 in this region 



oceanography, particularly the graphic repi-esentation as embodied in 

 the dynamic topographical chart, provide, furthermore, an easy and 

 efficient means of mapping currents over extensive ocean surfaces — 

 advantages which are bound to guarantee a great employment for 

 this science in future hydrographical surveys. 



DESCRIPTION OF A DYNAMIC TOPOGRAPHICAL CHART (CURRENT 



MAP) 



We now come to the description of a dynamic topographical chart, 

 a subject which has been reserved until the close of the various 

 methods of illustration, because, from its practical importance, it 

 merits especial emphasis. The basis for the construction of such a 

 projection depends fundamentally on the dynamic computations 



