36 
eye of the reader. Provided that the water is moving faster in the 
surface layers than in the depths, the rule follows: Loox 1n THE 
DIRECTION TOWARD WHICH THE CURRENT IS RUNNING, IN THE NorTH- 
ERN HEMISPHERE, AND THE LIGHTEST WATER WILL ALWAYS LIE ON 
THE RIGHT HAND. ‘The vertical differences of velocity may be calcu- 
lated from equation (f), see page 24, which is affected fundamentally 
by the values of temperature, salinity, and depth, at any two verticals 
in a plane and which it is important to note lies at right angles 
across the path of flow. 
GENERAL SUGGESTIONS FOR A PROGRAM OF HYDROGRAPHICAL 
SURVEY 
Ocean currents, it has been pointed out, may be determined by a 
distribution of temperature and salinity in a plane, the position of 
which is perpendicular to the flow of the water. Conversely, if no 
forces are found as represented by the position of the isosteres and 
isobars in vertical section, then there is no current at right angles 
to the plane of the section. It is easy to see, on the other hand, that 
a section parallel with the course of a current contains no informa- 
tion whatsoever regarding its movement. Hydrographical survey of 
extensive ocean surfaces involves in any event a large program of 
time and expense, and the task grows to considerable magnitude, 
especially when the work devolves upon the efforts of one vessel. 
An ideal program, of course, includes a maximum number of oceano- 
graphic stations distributed netlike over the area to be investigated, 
and wherein the promulgation of the work most nearly approaches a 
simultaneousness of observation. Unfortunately, the ideal survey 
rarely occurs, and it is usual that resort is made to lines of stations 
along a vessel’s track. Under such conditions it is apparent that 
before commencing the observational work the particular area should 
be studied carefully with respect to all previous, available knowledge 
of a hydrographical nature, remembering that the lines of stations 
in a program of dynamic investigation should run in such a manner 
that the sections secured approach most nearly to right angles across 
known or suspected currents. As an example let us take the region 
around the tail of the Grand Banks where there are two main move- 
ments. (1) The Labrador Current is the inshore set, which flows 
southward along the east side of the Grand Banks and to a variable 
distance around the ‘‘Tail.” (2) Offshore in the Atlantic basin the 
easterly moving masses of the Gulf Stream, guided by the trend of 
the bottom configuration, progress in a generally opposite direction 
to the cold water inshore. A program of dynamic investigation in 
this region should be based upon a series of lines of stations running 
offshore in a direction normal to the Grand Banks’ slopes as shown by 
Figure 18. Stations should be taken as close together (and repeated 
as often) as practicable in order that the influence belonging to tem- 
PS ee 
