46 
Proceedings of the Royal Society 
his specific gravities are reduced to 0°, to 4°, or to 15° ’56, or 
whether water at 0°, 4°, or 15° ’56 was taken as unity. It is 
therefore impossible to consider the results except as purely relative 
to the estuary in question, and no comparison between the different 
investigators can be made. 
The Cattegat, Skager Rack, Baltic, and north-eastern parts of 
the North Sea, have been made the subject of very careful and 
prolonged examination by various Danish and German scientific 
workers. Water samples have been taken regularly for a number 
of years at various points along the coasts, and from lighthouses 
and lightships at considerable distances from land. The results of 
the examination of these samples, from 1872 to 1881, is tabulated 
in conjunction with the meteorological conditions, especially with 
respect to rainfall, in a recently issued paper by the Commission in 
Kiel for the Scientific Investigation of the German Seas.* 1 
The general low densities of these waters, and the variations to 
which they are subject, make the conditions which obtain there 
not unlike those in an estuary, but they are in general more 
complicated and difficult of investigation. 
While it is fully realised that it will take years of consecutive 
observations to thoroughly settle the relations of the fresh and salt 
water in an estuary ; and that many conditions, such as the 
currents, law of the tides, and rainfall over the area drained by the 
principal river and its tributaries, must be taken into account, it is 
considered expedient to state the results observed in the six months, 
from June to December 1884, on the Firth of Forth. These 
results are purely preliminary, but as little attention has been 
given to such matters hitherto, they may prove of interest, and may 
lead to suggestions for improvements in the methods of carrying on 
the work. 
2. The Firth of Forth. 
The River Forth rises in the valley between Ben Lomond and 
Ben Venue, is joined near Stirling by the Teith, and gradually 
merges into the Firth of Forth, the precise point at which the river 
* Vierter Bericht fur die Jahre 1877 bis 1881, Berlin 1884, — Periodische 
Schwankungen des Salzgehaltes im Oberflachenwasser in der Ostsee und 
Nordsee, von Dr H. E. Meyer. 
