30 Fishery Board for Scotland. 



temperatures at the four corners of our quadrilateral, and attempt to 

 draw a series of isotherms leased on this information and nothing 

 more. It is plain that we shall get a schematic representation which 

 will correspond approximately to the actual facts, uncomplicated by 

 the various bends and irregularities which are found around the 

 various coasts. Look, for example, at our diagrammatic chart for 

 March. The temperatures at the four corners of our quadrilateral, 

 as found by interpolation from our Mean Temperature chart for that 

 month, are as follows : 



(60° N., 15° W.) 7-8° C. I 4-8° C. (60° N., 5° E.) 

 (50° K, 15° W.) 11-3° C. j 5-0° C. (53° N., 5° E.) 



Let us now, in this and all the other cases, reduce the temperature 

 in the north-western corner of our quadrilateral to nil ; the corre- 

 sponding temperatures will then be as follows : 



•0° C. I -3-0° C. 



3-5° C. I -2-8° C. 



In other words, as we pass from the north-western to the north- 

 eastern corner, there is a fall of 3° C. ; from the north-western to the 

 south-western corner, a rise of 3*5° C. ; from the south-western to 

 the south-eastern corner, a fall of 6*3° C. ; and from the south-eastern 

 to the north-eastern corner, a small or insignificant rise of 0"2° C. 

 The mean gradient over the whole area of the quadrilateral is, 

 accordingly, that which is shown in our diagram. In certain cases 

 the gradient thus roughly arrived at tallies better than in other cases 

 with that which we have before us in the full temperature chart ; 

 for instance in the month of February our chart is not at all good, 

 owing to the fact that the northern boundary which we have chosen 

 for it does not include the remarkable distribution of temperature in 

 the neighbourhood of 65° N. which causes the isotherms in that 

 region to make a sharp rectangular bend towards the south-east. 

 But on the whole, and as a rough illustration, I think this series of 

 diagrams is both useful and interesting, showing at a glance, as it 

 does, the steady change in the direction of the temperature gradient 

 from one season to another. 



It is not necessary that I should describe in words the twelve 

 monthly temperature charts which follow and to which the foregoing 

 pages form a general introduction. Let me simply say again, as I 

 said in the beginning of this paper, that these charts are published in 

 the hope that they may serve a temporary purpose, and in the belief 

 that they show a general approximation to the true conditions, such as 

 all our work in particular areas may gradually correct and improve, 

 until at length a series of mean values is arrived at which will be 

 generally accepted as a standard. 



In conclusion, I have drawn a series of isopleth diagrams, to 

 illustrate (1) the whole annual periodic changes of surface tempera- 

 ture along various meridians, from 20° W. to 5° E., that is to say, 

 from well out in the Atlantic to the eastern border of the North Sea ; 

 and (2) in two cases, namely, for 10° W. and for 0°, I have drawn 

 similar diagrams showing the differences or isanomalies as compared 

 with 15° W. 



