796 Proceedings of the Royal Society 
back of water above, but to rapid influx from the lower parts of 
the estuary. During the next two and a half hours the temperature 
is nearly uniform from the bottom to within one fathom of the 
surface, where there is a sharp rise. After five hours flood, while 
the lower strata are still falling in temperature, the surface fathom 
is rising rapidly; showing that ebb has begun above while flood 
continues below, the result being, of course, a shearing motion. 
The greater part of both flood and ebb tide is characterised by a 
strong current as nearly as possible of equal velocity at surface and 
bottom, but at the turning points of flood and ebb, and for about 
an hour before and after these crises, there is a shearing motion, the 
sliding of one layer over another. By this means the same 
condition of things is established at high and at low water, viz., a 
colder bottom layer, a warmer surface layer, and a short intermediate 
region of comparatively rapid change of temperature (see Plate 
XXVIII. fig. 4.) 
In the foregoing discussion for “rise of temperature” maybe 
substituted “ decrease of salinity,” and for “ fall of temperature ” 
“increase of salinity.” 
The 11 Leaky Tides .” — The fishermen at Kincardine speak of a 
tidal phenomenon which occurs both during flood and ebb. It 
consists of a temporary stoppage or reversal of the current ; when 
this takes place during ebb it is called the “ leaky flood,” and when 
during flood the “ leaky ebb.” We were not able to get any very 
precise information regarding it, and during our stay we were only 
once fortunate enough to see the effect. Prom such descriptions as 
we could procure, and from our observation of one leaky flood, the 
explanation seems to be as follows : — About an hour before calcu- 
lated low water at Kincardine the tidal current has become imper- 
ceptible in the lower part of the estuary, and shortly afterwards it 
turns and runs up. The stream of salt water going up the estuary 
meets the down-running current of fresher water as a wall, and 
serves to dam it back for some time, slackening the rate of ebb 
throughout the whole estuary, or even reversing it for a short time. 
Very soon, however, the difference in density of the two streams 
asserts its influence, the salter water penetrates the lower layers of 
the fresher, and flows up under it as a very diffuse and ill-defined 
wedge, while the surface layers, being released from the pressure, 
