366 
Part III, — Ninth Annual Report 
The mean specific gravity of surface water for 1890 was 102 3 '5 at 9 
A.M. and 1024'1 at 3 p.m., and for the first three months of 1891 it was 
1023*9 at 9 a.m. and 1024*3 at 3 p.m. As at Oxcar, the afternoon 
salinities were higher than those of the forenoon, and probably for the 
same cause. At the bottom the average specific gravity for the whole 
period was 1024*5 at 9 a.m. and 1025*1 at 3 p.m. The highest surface 
Frilinity was recorded as 1026*6 on July 20, 1889, the highest in 1890 
being 1026*1 on August 24. The lowest specific gravity recorded was 
1012*6 on January 15, 1890, the nearest approaches on other occasions 
being 1017-6 in December 1889 and 1018*0 in February 1891. The 
total range was thus 14*0. At the bottom the range was much less, 
being 7*5 ; the maximum was 1026*7 on July 20, 1889, and the mini- 
mum was 1019*2 on March 21, 1890. 
The curves of specific gravity at 10 a.m. are given from Table XV. on 
Diagram III, where they may be compared with those of other stations. 
The surface and bottom curves run parallel on the whole. When the 
surface curve comes to a minimum, on account of the great freshening of 
the water, the bottom curve ceases to follow it closely, showing that the 
freshening is mainly superficial. On the other hand, when the curves 
are at a maximum, they approach each other much more closely than the 
average, showing that the surface water has increased in salinity more 
rapidly than the bottom water. The curves show a distinct winter mini- 
mum and summer maximum, in which they resemble all the other curves 
for the east coast ; but the much greater range of the Abertay surface 
curve enables us to trace the seasonal variations more readily than in 
the other cases. Well marked maxima occurred in July 1889 and Sep- 
tendjer 1890, and a small maximum also appears in January 1891. The 
minima are in January 1890, when a spell of three months of low salinity 
began, and in November 1890, when the minimum was abrupt and short. 
Tiie exact fluctuations of salinity at any station must depend greatly 
on the rainfall for a few mo^iths previously and on the direction of the 
wind, so th-it annually recurring maxima and minima may be dis- 
placed considerably in successive years and yet be substantially similar 
in character. 
The specific gravity results classified according to tidal phase for sur- 
face and bottom are as follows : — 
[Table 
