of the Fishery' Board for Scotland. 



409 



of the bottom water is markedly above that of the surface water. A steady 

 fall of temperature took place during September and October, but from 

 the beginning until the end of November neither the surface nor the 

 bottom temperatures varied by a degree, and both rose slightly during 

 the first half of the month. In the first ten days of December the 

 temperatures of both upper and lower layers of water fell nearly 2°. 

 The air temperature curve shows a rapid rise at the beginning of this 

 period, and a very sudden fall of between 4° and 5° at the beginning of 

 December. 



It will be noticed, on studying fig. 5, that the bottom water was later 

 in being affected by this change of air temperature, and preserved the 

 effects of it for a longer time than did the surface water. 



A marked change in the curve of salinities and specific gravities, occurs 

 during this warm period, and shows that the surface water was relatively 

 very much fresher than the bottom water. This is another case of 

 abnormal physical conditions being very clearly shown by the. observa- 

 tions made at the Fishery Board's stations. It is very desirable that 

 the fishing returns for this period be carefully studied in connection with 

 its peculiarities. 



The mean specific gravity of the surface water at 9 a.m. was 1023 3 

 (2*87 per cent, of salts), and at 3 p.m. 1024-0 (3-00 per cent, of salts); 

 that of 3-fathom water 1023-8 (salts, 2*97 per cent.) and 1024*5 (salts, 

 3*08 per cent.) - while the bottom water was 1024'3 (3*05 per cent, salts) 

 in the morning and 10250 (3*18 per cent, salts) in the afternoon. The 

 density of the water during 1892 averaged almost the same as in 1891. 

 The water in the afternoon is markedly salter than in the morning, both 

 in 1891 and 1892. 



The maxima and minima for 1892 and 1891 may be compared from 

 the following table : — 



Mean Monthly Specific Gravities, Abektay, Maxima and Minima. 





1892. 





1891. 



Maximum — 

 Surface . . | 



Bottom . . -f 



Minimum — 

 Surface . . j 



Bottom . . \ 



9 A.M. 



3 P.M. 



9 a.m. 



3 P.M. 



1024- 4 

 (May, Aug.) 



1025- 0 

 (May, July, 



Aug. ) 



1021-5 

 (Nov.) 

 1023-3 

 (Nov.) 



1024- 8 



(May) 



1025- 5 

 (Aug.) 



1023- 0 

 (Nov.) 



1024- 6 

 (Nov.) 



1025-1 

 (July) 



1025-4 

 (July) 



1021-5 

 (Oct. and Dec.) 



1023*3 

 (Oct. and Dec.) 



1025-2 

 (July) 



1025-5 

 (July, Aug., Sept.) 



1023-4 

 (Dec.) 

 1024*7 

 (Dec.) 



There was therefore no marked difference between the salinity condi- 

 tions of the water at the mouth of the Tay estuary in 1891 and 1892; 

 but the surface water was hardly so dense in 1892 as in 1891, when the 

 extreme mean monthly specific gravities are considered. 



The actual extremes are — surface maximum, 1025*7 at 3 p.m. on 

 August 25; surface minimum, 101 3*3 on October 6 at 9 a.m.; bottom 

 maximum, 1026 0 on June 12, 13, and 19, and August 1 and 2; bottom 

 minimum, 1015-2 on October 6 at 9 a.m. 



The salinity curves of this station are shown in PI. XVIII. figs. 5 and G. 



