508 JUNCTION OF THE FRESH WATER OF RIVERS 
the salt water, and when the stronger current of the tide has 
reversed the direction of the stream, the salt water will be 
found occupying the bottom of the channel, while the fresh 
water will be suspended or diffused on the surface. This view 
of the matter occurred to me in 1811 ; but it was not until the 
29th of September 1813, that I had an opportunity of verify- 
ing the conjecture, by an examinatien of the waters of the 
Frith of Tay. 
Flisk Beach, opposite to which the experiments were made, 
is situated a considerable way up the Frith, being upwards of 
sixteen miles from Abertay and Buttonness, where the Frith 
of Tay actually joins the German Ocean. The channel of the 
Frith at this place is about two miles in breadth ; but upwards 
of a mile and a half of this extent consists of sand-banks, left 
dry at every ebb of the tide, and during flood, covered with 
from three to ten feet of water. These banks are separated 
from one another by deep pools, or /akes as they are termed, 
which occasion great irregularities in the motion of the cur- 
rents. The channel of the river is near the south side. It is 
about half-a-mile in breadth, having in the deepest part about 
eighteen feet of water, when the tide has ebbed, and upwards 
of thirty feet during flood. 
The apparatus which I employed was very simple: It con- 
sisted of a common bottle, with a narrow neck, having a weight 
attached to it. Besides the cord by which the bottle was low- 
ered, there was another connected with the cork, in such a 
manner, that I could pull it out when the bottle had sunk to 
the place of its destination. . The weather was favourable, and, 
on the day of the experiment, there was no wind to disturb 
the surface of the stream. 
With this apparatus, I proceeded to the middle of the chan- 
nel of the river, at Jow water, when the current downwards had 
ceased. 
