14 
surface, was a level plane. Other observations in this locality indicate 
that the 750 isobaric plane, however, is not always level, but a 
motionless state probably lies at some greater depth. The depth of 
750 decibars, nevertheless, approaches most nearly to the level where 
absence of motion may prevail of any depth of which the International 
Ice Patrol records; therefore, it has been employed in this paper as 
an illustration of the most accurate base upon which to calculate 
surface currents in the vicinity of the Grand Banks. 
B06 205 204 203 202 201 
Fa a a ee ae aaa 
DYNAMIC mms. 
Ovo NESEoL gone 
SURFACE or 
50 D-Bars (METERS) 
125 D-BARS (METERS). 
STATION ROG 
SuRFAcE 
- 50 D-BARS 
250 D-BARS (METERS). oe ett 
250 « — 
450 « 
750 « 
450 D-B4FS (METERS) 
75° D-BAFS (HETERS). 
Fic. 5.—The decrease in obliquity of observed isobaric surfaces with the observed increase in depth 
and based upon the assumption that the depth of 750 decibars was a level plane in which no motion 
prevailed. The figure includes a line of stations, 206 to 201, taken by the International Ice Patrol 
south of Newfoundland May 5-7, 1922 
The position of a level surface depends solely on the acceleration of 
erayity. Also, it has been pointed out that the depth to an isobaric 
surface depends not only upon gravity, but upon the specific volume 
of the overlying masses. Since we have already discussed gravity, let 
us now turn to the remaining term, specific volume. 
SPECIFIC VOLUME 
Pressure per unit area depends upon two variables, gravity and 
specific volume, but gravity being a more or less constant force, the 
agency which exerts the greatest influence to vary the pressure 
throughout the sea is specific volume. Specific volume has been 
defined as the volume of unit mass of any body. It is simply the 
