48 
Proceedings of the Royal Society 
3. Observations on the Surface Salinity in the Firth. 
It is assumed that the amount of total salts may he deduced from 
the density as if estuary water were ocean water, diluted with pure 
water. The assumption is that the percentage composition of the 
total salts is the same as regards their constituents, whether the 
water yielding them contain 1 or 4 per cent. The constancy 
of composition for ocean water was shown in 1865 by Forchhammer 
to be highly probable, and the researches of Tornpe, Schmelk, and 
other chemists of the Norwegian North Atlantic Expedition, 
crowned by Professor Dittmar’s exhaustive discussion of the 
“ Challenger ” waters, have established it as a definite certainty. 
This cannot be the case with estuary water, as the salts carried 
down by rivers are in quite different proportion to those found in 
the sea, and before the processes occurring there have had time to 
produce uniformity of composition; that is, where river water 
predominates, the proportion of the salts among themselves must 
vary. Consequently, until exact experiments can be made on this 
point, the interpretation of estuary densities by ocean-water tables 
must be taken with reservation. 
To get a preliminary view of the rate of freshening in the Firth 
of Forth, it was determined in September 1884 to make a monthly 
trip for collecting water samples from the entire firth ; and on the 
18th of September the “Medusa” proceeded from Inchkeith to 
Grangemouth for that purpose. Surface samples were taken every 
five miles (the positions are marked on the chart), and bottom 
samples at each alternate station. Observations were made both in 
going and in returning, and they are represented on the small 
diagram A (Plate IV.), the former as a dark, the latter as a light line. 
The tide was f flood at Inchkeith ; at Grangemouth, where we 
turned, it was two hours ebb ; and on the return to Inchkeith was 
f ebb. The weather was fine, but hazy throughout 
The intention to make the complete tour of the firth in one day 
had to be reluctantly relinquished, and the Inchkeith to May 
section was completed on the 25 th. Inchkeith was reached at 
10.30 a.m. with f ebb tide, and a strong south-westerly breeze. 
Surface samples were taken at the Stations marked cm the chart 
VIII., IX., X., and XI. At the May the tide was f flood, and a 
