Lyons — The DIstrilmtion of Mean Annual Rainfall. 355 



importaut problem in this counexiou. It is reasonable to suppose that over 

 a small area the conditions existing in the npper and middle layers of the 

 atmosphere are practically uniform at any time, and the rainfall distribution 

 must be almost solely decided by the orographical features ; hence the 

 relation of the one to the other may be worked out all the more definitely 

 for such limited areas. 



In only a few cases has this detailed study of local distribution of 

 rainfall been effectetl. Special reference must be made to the work of 

 Professor Hellmann,' in 1900, on the rainfall of East Prussia; to that of 

 Professor Schreiber on the rainfall of Saxony ; and to the study of Silesia 

 by Professor J. Partsch. In England the rainfall of the Lake District' was 

 investigated by Gr. J. Symons, f.k.s., in 1897. In recent years the Greo- 

 logical Survey of England and Wales has issued a series of memoirs* on the 

 Water-Supply of some of the English Counties. Each memoir contains a 

 valuable report on the rainfall of the county and a detailed rainfall-map by 

 Dr. H. El. Mill, Director of the British Rainfall Organization. 



Particulaks of Area Studied. 



The present investigation into the rainfall of the counties near Dublin 

 was undertaken by reason of the extremely marked yet simple relief features 

 of the area, and the comparatively large number of records available. 

 It proved, as anticipated, a very interesting study in local distribution, 

 presenting a considerable range, and very abrupt variation in rainfall. Apart 

 from its meteorological significance, the precipitation over this district is of 

 importance, as the area includes the catchments of some important rivers, 

 and the collecting-grounds of the Roundwood and Glenasmole Waterworks, 

 which supply the city and suburbs of Dublin. 



The limits of the area for investigation were decided, not by reference to 

 the irregular county boundaries, but by considerations of the configuration of 

 the country, and the records available. The boundaries are very approxi- 

 mately the meridians of longitude corresponding to 6° and 7° west, and the 

 parallels of latitudes 52° 42' and 53° 51' north. The length is about 82 

 miles, the average breadth 34 miles, and tlie area approximately 2800 square 

 miles. The region lies due east of the Great Central Plain of Ireland, and 

 is bounded on the east by the Irish Sea. To the south of Dublin the 

 Dublin and Wicklow Mountains form a continuous and clearly defined 



' RainfiiU Ciiart of East Prussia. Helliiianu; lierliii, 1900. 



- Zeitstlir. fiir Gewasserkunde, JBd. iii., 1900, p. 48. 



^ " British Eainfall," 1897. See also years 1867, 1895, 1896, 1898. 



^ Memoirs on Water-Supply. Geological SiuvBy of England ;iud Wales. 



bM2 



