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 
Fia. 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 representation 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 
