318 Proceedings of Eoyal Society of Edinhurgh. [sess. 
be attributed merely to experimental errors, but in great measure 
to actual differences in the relative proportions of the saline con- 
stituents in the various samples, and stated further that certain 
oceanic areas appeared to be characterised by positive or negative 
values for these differences. 
At that time, however, I was misled by a most unfortunate 
error of calculation in certain of my determinations of and 
was under the impression that differences similar to those of the 
“Challenger” samples could frequently be traced in samples collected 
near our own shores. This not only led me into certain erroneous 
speculations regarding the conditions obtaining in the North Sea, 
but prevented me from perceiving the full bearing of my results on 
the questions raised by the “Challenger” Eeport. 
It would serve no useful purpose to enter into a detailed 
explanation of the somewhat extraordinary circumstances which 
combined to prevent me from detecting an error for which, after 
all is said and done, I am responsible. 
I confine myself to stating that in those cases where in 
my Reports* samples of North Sea or Arctic water appear as 
giving values for D = 1 ’47, or thereabout, a constant correction of 
-fO '00447, applied to the logarithms of the values x? will bring 
these cases into perfect agreement with the others. This does not 
apply to the samples collected in the Cattegat, the Sound, the 
Baltic, and the Norwegian fiords. The high values (D) for these 
samples remain unaffected, and are to be explained by their con- 
taining salts derived from the land, as stated in my Report. 
The value T4556 for D, which I gave as characteristic of the 
Atlantic water round our shores, has recently been confirmed by 
Mr H. N. Dickson in a very able paper, to which I shall have 
occasion to refer again. 
As used by me, D has a more restricted significance than that 
given to it by Dittmar. It is defined by putting 
P oSq-IOOO ^ 
X 
where qSq = density of sea- water at 0° C. referred to that of pure 
water at the same temperature, x = total halogen calculated as 
chlorine per kilo, of sea-water. 
* Seventh Animal Report of the Fishery Board for Scotland (1888), p. 409. 
