of Edinburgh , Session 1884 - 85 . 
53 
the surface. It is also a curious fact that four samples of water 
from the firth beyond the Isle of May had a mean density of 
1-02514, scarcely greater than that at Station XII., and distinctly 
less than that at Station IX. The samples at the Isle of May were 
all collected, as it happens, during flood tide ; so that no current of 
the ebb carrying fresh water can be called in to account for the 
observation. It would almost seem as if the densities hinted at a 
maximum about Station IX. with lower densities on each side ; if 
the water of the Firth of Tay is fresher than that of the Firth of 
Forth a ready explanation suggests itself. 
In consequence of the way in which water-sampling trips were 
conducted, there were some Stations where the two samples were 
drawn at opposite phases of the tide. Inchkeith and Inchgarvie 
were usually in that position. Table IX. shows what difference 
was observed in the densities at different phases of the tides on the 
Table IX. — Variation of Salinity with Tides. 
_o 
Date. 
Density of Water. 
Alkalinity. 
Tides. 
02 
1 
2 
Dif. 
1 
2 
Dif. 
1 
% 
II. 
8-10-84 
1*01521 
1*00655 
866 
3J hrs. flood 
hrs. flood 
„ 
11-11-84* 
1*00474 
1*00070 
404 
11*1 
12*1 
-1*0 
2 hrs. ebb 
4£ hrs. ebb 
IV. 
8-10-84 
1*02414 
1*02131 
283 
| flood 
l flood 
V. 
18-9-84 
1*02461 
1*02425 
36 
50*4 
47*9 
2*5 
High water 
| ebb 
„ 
8-10-84 
1*02424 
1*02241 
183 
„ 
Low water 
„ 
11-11-84* 
1*02029 
1*01868 
166 
46*5 
42*1 
4*4 
„ 
„ 
VII. 
18-9-84 
1*02505 
1*02481 
24 
51*1 
48*2 
2*9 
| flood 
f ebb 
„ 
10-11-84*. 
1*02427 
1*02380 
47 
47*5 
50*1 
-2*6 
2J hrs. ebb 
2| hrs. flood 
IX. 
25-9-84 
1*02522 
1*02539 
-17 
1 hr. ebb 
Low water 
,, 
10-11-84* 
1*02508 
1*02495 
13 
51*3 
49*7 
1*6 
3| hrs. ebb 
| hrs. flood 
XI. 
7-10-84 
1*02544 
1*02566 
-22 
High water 
2 hrs. flood 
few occasions when these were sufficiently separated. It is of 
course very fragmentary, as the variations in the difference between 
high and low water must be considerable, but it is sufficient to 
indicate the general rule which prevails. The difference is by far 
the greatest in the upper reaches of the firth, and decreases more 
* River in flood. 
Stations. — II. Kincardine ; IV. Blackness ; V. Inchgarvie ; VII. Inchkeith. 
