172 



dry periods supposed to be connected with the above Saints' Days 1 

 Many such series of observations exist. Still we can only make 

 the comparison very imperfectly, from there being hardly two years 

 alike, not merely in respect of the actual amount of rain, but in 

 respect of the very unequal manner in which it is distributed over 

 a given month. In two cases where the actual quantity fallen is 

 the same, in one the whole may fall heavily during two or three 

 consecutive days occurring in any part of the month, whilst in the 

 other the rain may fall lighter and more continuously, or again 

 on several different occasions separated by short intei-vals. Under 

 such conditions it is only possible, by a careful balancing of a great 

 variety of instances, to work out as trustworthy a result as the 

 subject admits of. With a view then to this I carefully looked 

 over, in the first instance, a series of registers of the weather which 

 I kept when resident in Cambridgeshire for a period of nineteen 

 years, commencing with 1831 and ending with 1849, and which, 

 having been conducted with more regularity than any I have made 

 since, T thought might possibly throw some light on the matter. 

 The result is as follows : — I find that in most of the above years 

 the summer and autumn months taken together are divisible into 

 four — sometimes five — periods, more or less sharjily marked oflf 

 from each other, in which wet and fine prevail alternately. The 

 exact times at which these several changes take place are, from the 

 circumstance above mentioned, very variable, and occasionally they 

 are so iU-defined, the wet and dry alternating at such short 

 intervals, and those alternations continuing so long, that the above 

 periods are scarce distinguishable. When the three summer 

 months of June, July, and August have been all of this changeable 

 character, a dry period has usually set in in September, and some- 

 times lasted through October ; or, on the contrary, if they have all 

 been fine, the autumn has usually proved wet. When the whole 

 summer, and greater part of the autumn as well, have been wet, 

 dry and more genial weather has occurred in November, rarely 

 not till December. In one year, 1841, the wettest I ever knew in 

 Cambridgeshire, the wet set in about the middle of June, and, with 

 the exception of a period of ten days in August, there was scarce 

 any break to the unsettled weather during the rest of that year. 



