BIGELOW: EXPLORATIONS IN THE GULF OF MAINE. 77 
Knudsen’s (1901) tables and from Ekman’s (1910) tables of sea water 
under pressure. Such calculations are approximately correct arith- 
matically, but notice must be called to the fact that the probable 
limits of error are the sum of the two observational errors, first for 
salinity, 7. ¢., += .02 of salinity (p. 40), second for temperature, which 
is + .3° F, approximately .15°C. Now the sum of these errors has a 
considerable effect on the calculated densities, and for this reason 
the fifth decimal point is disregarded in the table. Of course a much 
higher degree of accuracy could be, and is, obtained with improved 
instruments, for example, during the North Atlantic cruise of the 
MicuHakEt Sars in 1910 (Murray and Hjort, 1912). But it would be 
misleading to claim better results with our instruments. 
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Fia. 34.— Curve of density in situ at Platt’s Bank (Station 23); Jeffrey's 
Bank (Station 25) and German Bank (Station 29). 
The correction for pressure has often been disregarded, especially 
in shallow water; but it can easily be applied from Ekman’s tables. 
In depths less than fifty fathoms it is of little practical importance, 
but by the time 100 fathoms is reached it is by no means negligible. 
For example, at Station 28, 120 fathoms, the density at the tempera- 
ture in situ without pressure correction, is 27.02; with pressure correc- 
tion, 28.03. In the accompanying table the pressure correction for 
depths less than fifty fathoms is calculated by the use of Ekman’s 
table IV alone, which is sufficiently accurate for our present purpose. 
The most important thing which the table and curves (fig. 34-36) 
show is that there was a steady increase of density at every station from 
the surface down to the bottom, which, as we now know, is the normal 
