352 



Appendices to Fifth Annual Report 



These show clearly the freshening of the water from north to south, which 

 is a marked feature of the Firth of Forth. It is very much less than the 

 freshening from east to west ; and of course it is irregular, depending in 

 amount for each cross section on the nature of the shores and the 

 proximity of rivers. 



Speaking generally, the action of tide on salinity in the Firth of Forth 

 is as follows : — From the mouth of the Firth to Inchkeith the result is 

 simply a to-and-fro movement of the water without any very apparent 

 consequences, as the salinity differs little from point to point. Above 

 Inchkeith the to-and-fro motion gradually changes into one of shearing. 

 The tidal water, from its superior specific gravity, tends to pass under the 

 lighter brackish water of the estuary, and to push its way below the 

 downward-moving stream of the river. After some time the river current 

 slackens, then stops, and finally turns, mixture with the salt water 

 becoming more complete. In the Forth these effects are observable at 

 Kincardine,* but they are seen to much greater perfection in large rapid 

 rivers flowing directly into the sea, such as the Spey.f 



The expeditions of the German gunboat ' Drache ' in 1882 and 1884 

 threw great light on the distribution of salinity in the North Sea, and 

 one of the most interesting results obtained by them is in direct relation 

 to the Firths of Forth and Tay. The line of 3*5 per cent, salinity 

 approaches the coast at Berwick and at Aberdeen, but between these 

 points it is carried far out to the north-east, and this freshening extends 

 even to the bottom. It does not as yet appear whether this freshening is 

 directly due to the Scottish firths, or to some more general cause as the 

 German observers suppose ; in the latter case the peculiar conditions of 

 the firths would be largely due to the freshened area of nearly uniform 

 salinity lying beyond them. 



All the trawling stations marked on the chart forwarded to me are in 

 water of approximately the same salinity (not varying more than 0-050 

 from 3*400 percent.), with the exception of that marked No. IV., which 

 is situated in water of an average salinity of rather less than 3*300 per cent. 

 This line is also that of the greatest variation of temperature, being 

 warmer in summer and colder in winter than any of the others. 



Alkalinity Observations. — The alkalinity of sea water is a measure of 

 the amount of dissolved carbonate of lime it contains. It is expressed by 

 the number of milligrams per litre of carbonic acid combined with 

 lime in the form of neutral carbonate. In order to make these figures 

 comparable, they are corrected to the value they would have for a sample 

 with the salinity of 3*50 per cent. That is to say, if alkalinity of 28 

 were found for a sample of 1 *75 per cent, salinity, it was multiplied by 

 2 to bring it to the standard of water of 3*50 per cent, salinity. The 

 figures obtained are given in Table IV., and shown graphically in 

 figure 3 (Plate XXI.). As in the case of salinity, the numbers for some 

 of the stations appear irregular, on account of the small number of cases 

 from which the averages were calculated. 



Table IV. — Mean Alkalinity of Firth of Forth. 



Station, II. III. IV. V. VI. VII. VIII. IX. X. 

 Surface, 51 -9 49-4 56-2 56*2 54-5 52 9 527 52*9 52*8 

 Bottom, • ... 52*1 ... 53*0 ... 527 



Omitting Stations II. and III., because the observations were few, the 



* Mill and Morrison, ' Tidal Variations in Estuary of Forth,' Proc. Roy. Soc. 

 Ed., xiii. pp. 790-799. 



t Mill and Ritchie, ' Physical Conditions of Rivers entering a Tidal Sea, as shown 

 ' in the case of the Spey,' Proc. Roy. Soc. Ed. 7 xiii., pp. 460-485, 



