358 Scientific Proceedifigs, Royal Dublin Society. 



J. Haun' in his analysis of the very long records of Padua, Klagenfurt, and 

 Milan, and was further confirmed by Dr. H. E. MilP in a study of several 

 long English records. It has been suggested tliat the particular value of the 

 35-year period is due to a periodicity in rainfall connected with the 35-year 

 Briickner cycle. 



This Records and the Methods of Reduction. 



The records used in the present investigation were, without exception, 

 those published in the volumes of " British Rainfall," the annual publica- 

 tion of the " British Rainfall Organization " founded about fifty years ago 

 by the late G. F. Symoos, F.R.S. The Organization at present includes nearly 

 6000 observers for the British Isles. The gauges are open to occasional 

 inspection, and all the returns are critically checked. Any doubtful return is 

 referred back to the observer ; and if no correction is made, and the doubtful 

 character remains, the return is queried if published or omitted altogether 

 from publication. 



There were available for the present paper seventy-three records of 

 varying duration, as shown by the following figures : — 



Over 35 years' duration 5 Records. 



From 30 to 35 „ „ 1 „ 



4 



,, 4 „ 



10 



12 



15 



., 22 „ 



The fundamental period adopted in the case of the long records was the 

 35 years from 1873 to 1907. It was considered desirable to end with the year 

 1907, so as to omit tlie very exceptional wet year 1872. The method of deal- 

 ing with the records of less than 35 years' duration so as to determine a mean 

 on the 35-year basis was that well established in rainfall work. The rainfall 

 over the short period was considered for the station in question, and also for 

 one of the nearest long or fundamental records. The short-period average for 

 the latter was estimated as a percentage of its known 35-year mean ; and the 

 short period average of the first station was increased or diminished in this 

 proportion to give its computed 35-year mean. This method is known to 



' Sitzungsb. del- k. Akad. der Wissensch. in Wieu, Mathera.-naturwias. Classe, vol. cxi., 

 part ii. a. 



2 Minutes, Proc. Inst. Civil Engineers, vol. civ., p. 'I'io. 



