SEA-FISHERIES LABORATORY. 231 



courses of the isotherms in the region North-east from 

 the Isle of Man are rather conjectural, for there are no 

 observations with the exception of those from the Solway 

 Light Vessels. South-west from the Isle of Man the 

 observations are fairly numerous, and enable us to draw 

 the isotherms with some degree of accuracy; while, 

 because of the greater uniformity of conditions in the 

 Channel between Ireland and the West coast of England 

 and the Isle of Man, the observations there, though fewer 

 in number, are still sufficient to determine the main 

 distribution of temperature. It is questionable whether 

 more numerous observations would make the task of 

 plotting the isotherms any easier. If we had a continuous 

 record of surface temperatures we should probably find 

 that minor irregularities would lead to dovetailing of the 

 contour lines, and the formation of " islands " of hotter 

 or colder water. The isotherms are to be regarded as of 

 the nature of smoothed curves, and probably represent 

 fairly the main facts of the distribution. 



The warmest part of the area in February, 1909, was 

 that part of the Channel in the fairway between the 

 Tuskar-Bishops line, and the latitude of Anglesey; and 

 the surface temperatures there varied from about 8'5° to 

 9°. The coldest region was that extending from Air 

 Point, in Cheshire, to the mouth of Morecambe Bay ; over 

 the greater part of this area the temperature was less than 

 4°. The central part of the Irish Sea was characterised 

 by great uniformity, the variation being less than 1°. It 

 will be seen that the isotherms bend round to the North- 

 east of Anglesey rather sharply, and that the temperature 

 gradient is steepest here. If a line be drawn passing 

 through the isothermal lines where the curvature is 

 greatest, it will be seen that this would correspond very 

 approximately to the axis of the Gulf Stream Drift, as 



