484 
Proceedings of the Royal Society 
very nearly constant; floods affect it slightly, but uniformly. It 
shows that in the “river proper” and “tidal” compartments there 
is rapid increase of density per mile of length, and much influence 
by tide ; while, as the firth is entered on, the increase of density per 
mile becomes less and less, and the tidal disturbance vanishes. 
The temperature rises steadily from the river out to sea in winter, 
and the bottom water is warmer than that at the surface ; in 
summer the temperature rises from the sea towards the river, and 
the surface water is warmer than that below. The annual range of 
temperature in the water is greater the further up the river observa- 
tions are made, hut the mean temperature appears to he nearly the 
same everywhere. 
Summary. 
The Spey, the most rapid river in Britain, is 120 miles long, and 
drains 1245 square miles. It flows into the Moray Firth — a bight 
of the North Sea — at Garmouth; .the river entrance is shallow, and 
subject to change of form and position by shifting hanks. 
Observations on the effect of tide on the mixing of sea and river 
water inside the bar are described. The exact vertical distribution 
of salinity was investigated by means of the hydrometer at intervals 
during the rise and fall of the tide, and the results are embodied in 
tables, diagrams, and curves. They show that the sea water slowly 
forces its way like a wedge between the river water and the bottom 
as the tide rises, and dams hack the water further up stream ; while 
the surface water always remains quite fresh, and a brackish zone 
separates the tw T o strata. When the ebb sets in the salt water runs 
out very rapidily, and before half-ebb there is only fresh water 
inside the bar. 
The salinity of the water in Spey Bay was studied during short 
trips in fishing-boats from Garmouth and Port Gordon, and by 
observations made along the shore. These are fully recorded. The 
bottom water of the hay was found to he of the density l - 02567 
on an average ; the surface water varied much in density ; and the 
river’s course could he traced as a stream sweeping to the north-east. 
The western margin of this stream was sharply defined ; on the east 
no abrupt change can he found, the river water gradually merging 
into the sea. During a spate the discoloration of the river water 
