50 
Proceedings of the Royal Society 
Inchkeith from 1 '02472 to 1*02403, and those at Stations VIII. 
and IX. from 1*02505 and 1*02518 to 1*02458 and 1*02508 
respectively. 
The December trip did not take place till the 25th, when my 
friend Mr T. Morton Ritchie was good enough to take charge of the 
eastern excursion. „ The day was fine, with a north-easterly breeze, 
and a slight swell. The tide was two hours ebb at Station VII. 
going, and one hour flood at the same place returning. On the 27th 
the yacht started for Alloa, but the morning, which was hazy, gave 
place to a day of fog, and it was impossible to proceed beyond 
Inchgarvie. The 29th and 30th were also misty, and this portion 
of the trip had, very reluctantly, to be dispensed with. 
The curve D (Plate IV.) shows that the water had returned to 
its former value after the diluting effect of the floods of November. 
The effect of the tide obscures the changes of salinity to a certain 
extent in these monthly cruises, but although the data are so few 
they are sufficient to show that between Inchkeith and the Isle of 
May the tidal effect is relatively slight, and the variations in density 
very gradual, though perceptible ; while from Inchkeith to Alloa the 
tidal effect increases with every mile, and the rate of change 
becomes more and more rapid. Tables VI. and VII. give the 
figures observed in these consecutive trips. 
In order to make some attempt at neutralising the influence of 
tides, the mean was taken of all the observations made since June 
at each of the Stations. These were made at all states of the tide, 
and in all weathers that the yacht could stand, and although they 
are not very numerous, and do not extend over more than seven 
months, they give some idea of the alteration in salinity with 
position. 
The means are embodied in the diagram (Plate V., E), on which 
the calculated amount of total salts is also represented. It plainly 
shows that the parts of the firth to which least attention has, as yet, 
been given, those west of Inchkeith, are the most deserving of study, 
for there the changes are large and rapid. 
The maximum, minimum, and mean density observed at each 
Station, together with the number of cases which give the mean, are 
tabulated. (Table VIII.) 
