ON THE RAINFALL OF THE BRITISH ISLES. 261 



memberiiig that the 1860-69 decade has shown the various features in a less 

 marked degree than the decade 1850-59. 



In order to facilitate an acciirate determination of the months in which 

 the maximum and minimum rainfall usually occur we have compiled 

 Table III., which gives the mouths of maximum and minimum respectively 

 for two complete decades (for England, Scotland, and Ireland), adopting the 

 same subdivision into districts, and grouping according to amount of annual 

 fall, as in the previous Tables. 



An abstract of the results of Table III. is given as Table IV. 



These two Tables are very instructive, and afford information respecting 

 the distribution of the epochs of maximum and minimum previously unat- 

 tainable. 



The general features will be better understood by an examination of the 

 Tables than by any description ; and we therefore confine ourselves to re- 

 marking that the essential chfference between the two decades is that in 

 1860-69 July, as a month of maximum rainfall, has disappeared altogether, 

 and April has become more frequently that of the minimum. In fact during 

 the last ten years April has been the di'iest month at most stations in the 

 British Isles, while in the previous decade this distinction was pretty equally 

 shared by February and May. 



The gradual retardation of the epochs of maximum and minimum as the 

 annual amount of rainfall increases, is also clearly shown by the upper por- 

 tion of Table II. ; while in the lower or departure portion of Table II. it is 

 very instructive to observe the change of sign as the average total rainfall 

 increases. 



With a view to determining whether the same relative monthly values 

 are found at the same station in all decennial periods, we have selected 

 seventeen registers, each extending over at least forty successive years, while 

 four extend over fifty, and one over sixty successive years, and reduced them 

 in the same manner as the 1860-69 values. These are given in Table V. ; 

 and the result can hardly be called satisfactory. They show the same 

 general features as the two decades which have been discussed in detail, 

 such as the larger percentages in winter months in wet districts, and in the 

 summer and early autumn in dry districts ; but the months of maximum 

 and minimum shift about to an extent which would not be expected, con- 

 sidering that each value represents the average of ten years. An examina- 

 tion of these records, all embracing more than one third of a century, proves 

 that, however steady the ten-yearly average amount of rain may be, its dis- 

 tribution over the mouths is iiot so by any means; so that, as far as our 

 present investigations go, it is impossible to lay down any general law as to 

 the precise month of maximum and minimum fall. 



It has been the custom of this Committee to follow the practice inaugu- 

 rated by Mr. Symous before their appointment, and give biemiially details 

 of the monthly faU of rain over the British Isles. As this practice has 

 several advantages, your Committee are unwilling to depart from it, and 

 therefore leave the detailed discussion of the rainfall of 1872 until next 

 year ; at the same time, as the total was in many districts excessive, and in 

 several localities unprecedented, they have instructed their Secretary to pre- 

 pare for the Bradford Meeting a map showing the more remarkable general 

 features, and briefly to explain it. But as the subject will be discussed at 

 length next year, they do not make cither the map or remarks a part of the 

 present Keport, 



