25 
Tt is assumed that the specific volumes in situ have been calculated 
from the tables, as based upon the temperature and salinity records 
from the observed depths, viz, 0, 50, 125, 250, 450, and 750 meters. 
The values of p are, for all practical purposes, equal to the depth in 
meters—that is, at a depth of 750 meters the pressure is 750 decibars 
(see p. 11). In order to compute as accurately as possible the value 
of D (the dynamic depth) for the vertical AC, it is necessary to 
consider the change at frequent depths which occurs in the value of v 
(the specific volume). In order to comprehend the method of mathe- 
matical computation customarily followed, e. g., p. 28, it will be help- 
ful to regard Figure 9. 
fo) WM “My Ve Mo 
Fic. 9.—A graphic means of illustrating the mathematical integration 
customarily employed in computing the dynamic depth to a given 
observed pressure beneath the sea surface 
The area MNPO (assumed equal numerically to D,) is formed part- 
ly by the curve NP, which represents varying values of v, and the 
side MO, which indicates the scale of pressure. The value of D,, 
therefore, represented by the area MNPO is equal in value to the 
sum of all the smaller areas d,, d,, d,, d,, and d;. The area d; (and 
the values of all the other small rectangles in similar manner) may, 
with sufficient accuracy, be put equal to 
(42%) 
VU 
De= (%5")dps + (*5™)dpa+ (5 dpa + (*S™ apa + (Sp, 
which equals the value of the gravity potential, relatively to the sea 
surface, expressed as a depth in dynamic meters at which the pressure 
or 
