of the Fishery Board for Scotland. 



353 



alkalinity appears to vary inversely as the salinity, and to be greatest on 

 the surface. Other observations have shown that in the neighbourhood 

 of rivers the alkalinity of surface water is greater than that beneath. 



Temperature Observations. — The temperature of the water was observed, 

 as well as the salinity, in all cases, and much more numerous experiments 

 were made. The extreme simplicity of the submarine configuration of 

 the Firth of Forth leads one to expect a correspondingly simple distribu- 

 tion of temperature, and this has been found to be the case. All the 

 temperature observations which were made are not yet in a state for dis- 

 cussion, but the general principles are perfectly plain. In spring, about 

 the month of April, the whole river and Firth in its length and breadth 

 and depth are at one temperature, 40° to 43°, the precise degree of 

 warmth apparently varying from year to year. Along the central line of 

 the Firth heating goes on rapidly as the season advances, the surface heat- 

 ing more quickly than the lower strata, and the river more rapidly than 

 the sea. Consequently, a typical summer distribution is arrived at, in 

 which there is a continuous gradient of temperature from river to sea, and 

 from surface to bottom. The temperature at Alloa in August may be 

 about 60°, that at the Isle of May 55°, and the bottom water from 3° to 2° 

 colder. After the autumnal equinox cooling sets in, and this is most rapid 

 in the landward reaches and on the surface, slowest at sea and on the bottom. 

 As a result, a state of uniformity is reached in October or November, with 

 a temperature of about 50° from river to sea and from surface to bottom ; 

 then, as cooling goes on, the river becomes coldest, and in January or 

 February the minimum is reached, and the condition then is a uniform rise 

 of temperature from river to sea and from surface to bottom. As spring 

 advances heating ensues, and once again a uniform temperature is attained. 

 Figure 6 (Plate XXII.) illustrates these seasonal changes, but it is drawn 

 rather as a diagram than an expression of observed facts. In figure 7 the 

 annual progress of temperature is shown for each of four divisions of the 

 Forth. The first curve embraces all observations between Alloa and 

 Grangemouth, and shows a minimum in February and maximum in July; 

 the second curve is for the space between Blackness and Oxcar, its 

 minimum is in January, its maximum in August ; the third and fourth 

 curves represent the spaces between Inchkeith and a line ten miles west 

 of it, and between Fiddra and the Isle of May respectively. The data are 

 those for the one year, May 1884 to April 1885. All the curves cross in 

 April and October, that with the lowest maximum having the highest 

 minimum, and the range increasing uniformly with distance from the sea. 

 The mean annual surface temperature for all stations is about 47 0, 5, and 

 this agrees with observations continued for many years at Dunbar, North 

 Berwick, and Trinity. The latter results showed a slight increase in 

 mean annual temperature, not exceeding 0°'5, towards the open sea. 



The temperature of water is much influenced by the land that surrounds it. 

 A shallow river responds more rapidly to changes of atmospheric tempera- 

 ture or amount of sunshine than the sea does, and, as a rule, the shallower 

 the water the more quickly and powerfully is it affected. Thus, in 

 summer, the southern margin of the Firth of Forth is very much warmer 

 than the northern, and in winter very much colder. As rivers usually 

 enter the firth where the depth is slight and the bottom shelves very 

 gradually, great variations of temperature are usually associated with the 

 freshest water, and with that most variable in salinity. While there can 

 be no reasonable doubt as to the applicability of the general principles 

 we have stated, much still remains to be done before a thoroughly satis- 

 factory knowledge of the temperature variations of the Firth of Forth can 

 be attained. 



