159 



Physical Investigations. 



Preliminary Paper. 



By 

 H. N. Dicksou, F.B.S.E. 



With Plate XI. 



It may be taken for granted tliat^ apart from its purely scientific 

 value, a knowledge of the physical conditions affecting the waters 

 of the sea has been shown to throw considerable light on many im- 

 portant economical questions. In its bearing on fish and fisheries, 

 the inquiry may be said to have reached a point where it is conclu- 

 sively shown that there is a problem to solve. 



In a report of the Herring Committee of the Scottish Meteoro- 

 log'ical Society we find the following stated as preliminary re- 

 sults : — " If, during the herring season, there be a district where, 

 from any cause, the temperature of the sea is lower than in sur- 

 rounding districts, the catch of herrings is heavier in that district ; 

 and conversely if there be a district where, from any cause, the 

 temperature of the sea is higher than in surrounding districts, in 

 that district the catch of herrings is less. Among the causes which 

 bring about a local increase or decrease of sea temperature, the chief 

 are clouded or clear skies in respective disti-icts, according as these 

 occur during the day or during the night. 



'' The above refers to local fluctuations of temperature during the 

 fishing season, when the temperature of the sea is high. It appears 

 from the observations of past years that the herring seasons have 

 closed about the time when the temperature of the sea in its annual 

 fall has fallen generally to 54'5° F. It is of importance to ascer- 

 tain how far this relation exists from year to year and in different 

 districts. 



'' Another important point is the relation of surface temperature 

 to bottom temperature, and the relations of the deepest parts of the 

 sea to the positions of the fishing-grounds. It is found, for in- 

 stance, that when the surface temperature is high — higher than 

 lower down — the fish, if any can be caught, strike the nets far 



NEW SERIES. VOL. II, NO. II. 13 



