SEA-FISHERIES LABORATORY. 241 



low temperature, this specific gravity would be lower 

 still. It is onl}' on very rare occasions that specific 

 gravities less than 1024 are observed in the open sea. 

 Of course, very low values are sometimes obtained in 

 estuaries. Thus, on 16th November, 1901, at low water, 

 a specific gravity of 10171 was taken at Liverpool 

 Landing Stage. In the case of the Blackpool determina- 

 tion, which I refer to here, the cause was the exceptionally 

 heavy floods which had taken place in both the Hibble 

 and the Wyre about a week previously. The fresh water 

 poured down from these rivers was, even a week later, 

 forming a surface layer on the adjacent sea area. What 

 the reading 1021*8 of the hydrometer means is that the 

 normal sea water on the surface had become mixed with 

 (roughly speaking) about 20 per cent, of fresh water. 



