54 
Proceedings of the Royal Society 
and more gradually. Beyond Inchkeith the difference is little 
noticed, in fact the water is found to he sometimes denser at a lower 
state of tide. This effect may he due to currents, which were not 
taken account of in this preliminary investigation. The rate of 
change of density with the tide decreases very rapidly at first. At 
Kincardine, the difference touches the second place of decimals ; 
calling the density of pure water 10,000, it is 100, at Inchgarvie it 
is about 15, at Inchkeith 4, and beyond Inchkeith about 1 ; that is, 
1 in the fourth decimal place by ordinary notation. 
The temperature observations made on the monthly trips have 
not been alluded to here ; they are intended to form a separate 
paper. It w r as found, speaking generally, that in summer the 
temperature of the surface water was highest at Alloa, and steadily 
fell as the Isle of May was approached ; the rate of fall becoming 
more and more gradual. In winter this state of affairs is inverted. 
The water at Alloa is the coldest, and the temperature rises more 
and more gradually towards the May. The difference also is much 
greater between the summer and winter temperatures at Station I. 
than at Station XII. Bor example, at Queensferry (Station V.), on 
July 31, the surface temperature was 58° - 2 Fahr., on December 27 
it was 41° *2 Fahr., a range of 17° Fahr. At the May, on June 
11, the surface temperature was 50° T Fahr., and on December 25, 
within six miles of the May, it was 43° ’8, a range of 6°* 3. 
The change of temperature produces a corresponding change in 
the density of the water in situ , which has important bearings on 
convection currents, and which must also influence the rate of 
mixture of sea and river water, especially as the temperature of the 
river water is, in winter, usually below that of its maximum density. 
4. Surface Water Density at the Marine Station. 
The Scottish Marine Station has a floating laboratory moored in 
the centre of the submerged Granton Quarry. The entrance is on 
the western side, and at high water it is continuous with the firth 
for a considerable breadth. At low water the channel is dry, and in 
front of it is a broad tract of sand extending out to Cramond Island, 
The River Almond flows into the firth just to the west of Cramond 
island, at low water. It is about two miles distant from the 
quarry. 
