822 
BULLETIN OF THE BUREAU OF FISHERIES 
alkaline seas, as might have been expected from its comparatively low salinity and 
temperature. Within the gulf, however, the pH from station to station does not 
correspond to the differences in salinity or in temperature; neither have I been able 
find any definite parallelism between the pH and the abundance of diatoms — cer- 
tainly no decided rise even at the times and stations when these pelagic plants are 
flowering most freely. In short, the volume of water is too large and its circulation 
too free for any given flowering to reflect its active photosjmthesis by an appreciable 
local rise in pH. 
The fact that in March the deeper of two samples was in several cases the 
more alkaline, but that in May the reverse was true, may be significant, the phyto- 
plankton being most abundant in the well-illuminated strata near the surface. It is 
not improbable, also, that a larger number of observations carried out through the 
the year would reveal a seasonal fluctuation of pH, with the maximum in early 
spring and summer following the vernal flowerings of diatoms and the summer mul- 
tiplication of peridinians, such as occurs in the Irish Sea 23 (Moore, Prideaux, and 
Herdman, 1915; Bruce, 1924). 
VISUAL TRANSPARENCY 
Measurements of the transparency of the water were taken at 18 stations dur- 
the summer of 1912 with the ordinary “Secchi” disk — a metal plate 14 inches in 
diameter, painted white, and rigged with a bridle, so that it hangs horizontal. This 
is viewed through a water glass 24 while being lowered, and the depth at which it 
disappears from view is recorded. 
In the clearest water the disk was visible to 8.2 fathoms, but at most of the 
stations it disappeared at 4 to 5 fathoms. Local variations in transparency did not 
parallel the variations in color (p. 823), for while the water was most transparent 
when bluest, it was not least so where greenest, but where the percentage of yellow 
was only 20 (station 10038). 
The transparency does not measure the penetration of sunlight, for water 
cloudy with silt or with diatoms may still be translucent, like ground or opal glass, 
though transparent to only a small degree. 
Transparency, in meters 
Date, 1912 
Station 
Transpar- 
ency 
Date, 1912 
Station 
Transpar- 
ency 
July 11 
10004 
6.4 
Aug. 15 
10031 
7.3 
July 17 
10011 
11 
10036 
7.3 
July 23 
10012b 
11 
Aug. 21 
10037 
7.3 
July 24 
10014 
11 
10038 
5.5 
July 25 
10015 
8.2 
Do 
10039 
11 
July 26 
10016 
6. 4 
10040 
9. 1 
Aug. 7 
10022 
13 
Aug. 29 
10043 
9. 1 
Do 
10023 
15 
Aug. 31 
10044 
9.1 
Aug. 8 
10025 
12 
23 See Nelson (1924) for an account of rapid diurnal variations of pH in the estuarine wafers of New .Tersey , 
!i The use of the water glass is necessary to escape the effect of reflections from the surface. 
