Hydrometrical Observations. 387 
on the top during the whole of flood as well as ebb tide. The apparatus 
consisted of a bottle or glass jar, the mouth of which measured about 24 
inches in diameter, and was carefully stopped with a wooden plug, and 
luted with wax ; a hole, about half an inch in diameter, was then bored 
in the plug, and to this an iron peg was fitted. To prevent accident in 
the event of the jar touching the bottom, it was coated withflannel. The 
jar so prepared was fixed to a spar of timber about 20 feet in length, 
which was graduated to feet and inches, for the conveniency of readily 
ascertaining the depths to which the instrument was plunged, and from 
which the water was brought up. A small cord was attached to the iron 
pin for the purpose of drawing it at pleasure for the adinission of the 
water. When an experiment was made, the bottle was plunged into the 
water: by drawing the cord at any depth within the range of the rod to 
which it was attached, the iron peg was lifted or drawn, and the bottle 
was by this means filled with water, of the quality at the depth to which 
it was plunged. The peg was again dropped into its place, and the ap- 
paratus raised to the surface, containing a specimen of water. In this 
manner, the reporter ascertained that the salt or tidal water of the ocean 
flowed up the channel of the River Dee, and also up Footdee and Tor- 
ryburn, in a distinct stratum next the bottom and under the fresh water 
of the river, which, owing to the specific gravity being less, floated upon 
it, continuing perfectly fresh and flowing in its usual course towards the 
sea, the only change discoverable being in its level, which was raised by 
the salt water forcing its way under it. The tidal water so forced up 
continued salt, and when the specific gravities of specimens from the bot- 
tom, obtained in the manner described, were tried, and compared with 
those taken at the surface, by means of the common hydrometer of the 
brewer (the only instrument to which the reporter had access at the 
time), the lower stratum when compared with that at the surface was 
always found to possess the greater degree of specific gravity due to salt 
over fresh water.” 
The appearance of the fresh water floating on the surface of the sea, is 
no doubt familiar to most persons. It occurs at the mouths of many of 
our rivers, and is most apparent when they are in flood, from the brown 
tinge given to the water, which is easily discoverable for many miles at 
sea. The great American rivers furnish many remarkable instances, par- 
ticularly La Plata and the Amazons. On this subject, the following 
passage from the work* of Father Manuel Rodriguez, a Spanish Jesuit, 
is interesting, and its correctness, as regards the extent to which the in- 
fluence of the river is felt, has since been corroborated by the investiga- 
tions of Colonel Sabine.t ‘‘ This river,” says Rodriguez, in speaking of 
the Amazons, “ is like a tree ; its roots enter as far into the sea as into 
* FE] Maranam y Amazonas. Madrid, 1684, p. 18. 
+ An Account of Experiments to determine the figure of the Earth, as well ag 
on various other subjects of philosophical inquiry, by Edward Sabine, London, 
1825, p. 445. 
