JOS 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 examination 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 ta ten feet of water. These banks are separated 

 from one another by deep pools, or lakes 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 low water, when the current downwards had 



ceased 



