(550 EIGHTH PACIFIC SCIENCE CONGRESS 



Strait, as shown in Figure 8, it was noted that the index salinity re- 

 curred within 0.2°/oo S at the upper limit of the zone at every station 

 in the vicinity of the Fraser River. The plan and cross-sections of the 

 data were interpreted by contours of depth of this index. This illus- 

 trates the structure of the region much more realistically than the usual 

 contours of arbitrary salinity values. 



Indication of Errors 



In the course of plotting the data occasional lone points were found 

 that deviated from the log-plot defined by other points above and 

 below. On checking the calculations and data, errors were found, or 

 were possible, in practically all cases. The accumulation of such expe- 

 rience has led to the policy of discarding single observations that do 

 not coincide with the log-plot. 



Calculatiofi of Dynamic Height 



The calculation of dynamic height requires the mean density 

 through the column of water defined by a serial observation. The 

 usual procedure is to compute the mean density of each sample and 

 integiate with respect to depth. Having established the validity of the 

 log-plot as the best representation of the data, it is permissible to reduce 

 the labour by calculating the mean density in each w^hole zone. 



Where the limits of the zone from the surface downwards are Zj 

 and Z2 the mean density (a) in a zone may be written 



' ^ -i J. ' 



dz (4) 



where o- is the density in situ of the water at the limits z^, z.^, etc., ex- 

 pressed as (p — 1)1000. But it has been shown that 



a - k log z -{- c (1) 



Setting this in Equation 4 



k rz» 



<^ - "J J (log z -f- c)dz 



= ^ [z,(logz, 4--i_l)_z,(logz, -f-i.-!)] 



in which /; and c may be evaluated in terms of the data as shown in 

 Equations 2 and 3. Whence the expression becomes 



(5> 



[z, (log z, + £- - 1) - z, (log z, + ± _1)] 



log Z3 — log Zi 



