14 Tattersall & Coward, Fatma of RostJieme Mere. 



date differs according to the tales of the various people 

 who never hear it ; it varies between Easter Eve and 

 Christmas Eve. A reference to the tradition can be 

 found in Henry Green's " Knutsford." " 



It is interesting to note that a very similar legend is 

 told of the largest of the Cheshire meres, Combermere. 



Temperature. 



The temperature of the surface water was taken on the 

 occasion of each visit to the mere from May, 19 12, to 

 November, 19 13. The temperatures are set out on the 

 following chart, and the resulting curve gives a very fair 

 idea of the range of temperature to which the mere is sub- 

 ject. The winter of 1912-13 was comparatively mild, and 

 the temperatures recorded were never very low. On the 

 other hand, we believe that in many years the temperature 

 of the water in the summer must rise above the highest 

 figures we obtained, 19° C. The maximum temperature 

 of 19'' C. was reached in July, 1912, and August, 1913, 

 and the minimum, 4'2°C., in January and February. 



In the matter of temperature, Rostherne Mere shows 

 a similar range to that noted for Lough Neagh by Dakin 

 and Latarche,'^ and a considerably greater range than that 

 exhibited by the Scotch lakes, in which the annual range 

 is only about 5 — I5°C. This is to be explained by the 

 fact that the Scottish lakes are very much deeper than either 

 Lough Neagh or Rostherne, and have relatively much more 

 steeply sloping shores. The annual range of temperature 

 is an important factor in determining the nature of the 

 plankton of a lake, and it is quite possible that the absence 

 of " water bloom " in the Scotch lakes and its regular 



>' Green, il. "Knutsford, its Traditions and History," p. 92. 

 London, 1859. 



^■- Proc. K. Irish Acad., Vol. XXX., Sec. B, No. 3, 1913. 



