masses mix in a sufficiently constant proportion so that the mixed 

 water can be regarded as a virtual water mass. Mean T-S curves 

 for these three water masses have been derived from observations 

 made during- the 8-year period 1934-41. Conditions found during 

 the recent postwar years were compared with these prewar means 

 for want of any better normals. We now have a postwar series 

 of observations of comparable length made during the 9-year 

 period 1948-56. The mean T-S relationships for each of the three 

 water masses is shown for each of the two periods in figure 16. 



43 



