of Edinburgh , Session 1884-85. 61 
1024:0 at the bottom and 10220 at the surface. On November 11 
the bottom density was 102476 at low water, the surface was only 
101863, a difference of 000613. This was evidently due to the 
unusual rapidity of the surface current caused by the swollen rivers, 
being sufficient to retard the process of diffusion between the two 
kinds of water. As an ordinary thing, the bottom water at Inch- 
garvie is nearly as salt as that at Inchkeith, while the surface water 
is much fresher ; in fact, in a heavy flood there is river water on 
the surface and sea water below it. The following comparison of 
water from half the depth with that at the bottom and surface 
shows that the denser water extends at any rate to half the depth, 
so that one would he inclined to view the heavy sea water filling up 
the hollow as part of the river bed, over which the fresher upper 
water flows. Experiments with a current gauge at various depths 
would he certain to give much valuable information on this subject. 
Bottom, 
Half-Depth, 
Surface, 
The salinity of the 
of the surface. 
a. b. c. 
1-02478 1-02455 1 -02448 
1-02461 1-02440 1 -02426* 
1-02424 1-02324 1-02425 
bottom water was never found less than that 
6. The Alkalinity of the Firth of Forth. 
Table XI Y. gives particulars of 98 determinations of alkalinity 
arranged according to magnitude. 
Speaking roughly, it shows that waters having an alkalinity 
under 40 (that is in which there is less than 0U4 grammes of 
carbonic acid as carbonate of lime per litre) have a density 
under 1*0200, alkalinities under 25 correspond to densities under 
1-0100. The only strikingly anomalous case is that of sample 
No. 189, a bottom water from off Alloa, when the river was low 
and very dirty. The density was 1*00146, the alkalinity 47*9, 
which usually corresponds to a density of 1 -024. The presence of 
sewage in the river might account for this observation to some ex- 
tent, but more probably it is due to the presence of particles of 
calcium carbonate, to which cause the very exceptional alkalinities 
of Nos. 94 and 70 may also be referred. 
* Uncertain. 
