350 
Proceedings of the Royal Society 
This table shows that, as on the Forth, bat in a more pronounced 
manner, the effects of tide and of flooding in the river are very 
considerable in the upper part of the estuary ; so much so that the 
observations recorded above are of almost no use in determining the 
normal salinity of the Firth of Tay at any point. The serial 
densities observed on each day when plotted in a curve, show a 
state of matters very similar to that existing in the Forth. From 
Newburgh to the Abertay Lightship corresponds in regard to 
surface salinity with the stretch of the Forth from Alloa to Queens- 
ferry, but the closer proximity to the open sea produces its effect 
in raising the salinity of the bottom water about the mouth of the 
Tay. 
It appears that in the Tay, while the salt sea water runs up along 
the bottom so as to produce a very marked difference in the density 
of the bottom and surface water at the Lightship, it is rapidly 
mixed as it passes on, no doubt on account of the shallowness of 
the channel and the strength of the current. 
The position of the highest point to which brackish water extends 
in the Tay at high water is effected by the amount of tidal rise and 
of flooding in the river. In summer it is said to be always undrink- 
able at high water at Newburgh; while some fishermen say that 
the salt can be tasted at Perth during very dry summer weather and 
at high spring tides. 
Although not connected with the salinity, the colour of the water 
when looked down into on a clear day may be noted. At New- 
burgh it is a clear amber-brown, which lower down becomes a little 
muddy, and as the salt manifests itself a green tint is added, so that 
at Tayport it is an exquisite olive-green, a colour which prevails 
with a lessening of the brown ingredient right across St Andrews 
Bay. This contrasts with the pale muddy green of the upper 
reaches of the Firth of Forth, which gives place to a deeper and 
more transparent blue-green tint as the Isle of May is approached. 
The effect is very much that which would be produced if a green 
liquid ( e.g ., solution of dark transparent cupric chloride) were diluted 
gradually with water for the Forth, and with a brownish-yellow 
liquid ( e.g ., very dilute ferric chloride solution) for the Tay. 
